kvm-27 vs 28 I/O speed

kvm-27 vs 28 I/O speed

[Dave Hansen]

I've noticed that some of my tests run *MUCH* slower in kvm-28 than in
27.  I'm sure that wall time is pretty wonky in the guests, but it is
much slower in real-world time as well.

Here's a little test to create a 32MB zeroed file with dd.  Here it is
from kvm-27 (this took ~5.5 seconds on my wristwatch):
33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec)
33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec)

Here's the same thing from kvm-28 (~80 seconds on my wristwatch):
33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec)
33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec)

Same host kernel, same kvm kernel modules (from kvm-28) same guest
kernel, same command-line options, same disk image.

Any ideas what is going on?

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Dave Hansen wrote:
> I've noticed that some of my tests run *MUCH* slower in kvm-28 than in
> 27.  I'm sure that wall time is pretty wonky in the guests, but it is
> much slower in real-world time as well.
>
> Here's a little test to create a 32MB zeroed file with dd.  Here it is
> from kvm-27 (this took ~5.5 seconds on my wristwatch):
> 33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec)
> 33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec)
>
> Here's the same thing from kvm-28 (~80 seconds on my wristwatch):
> 33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec)
> 33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec)
>
> Same host kernel, same kvm kernel modules (from kvm-28) same guest
> kernel, same command-line options, same disk image.
>
> Any ideas what is going on?
>   

Is this repeatable?  I don't see anything in kvm-27..kvm-28 that 
warrants such a regression.

Things to check:

- effect of pinning the vm onto one cpu (with 'taskset')
- does any counter in kvm_stat behave differently

If you are using qcow, maybe the effect is due to the first test hitting 
a hole and the second being forced to read from disk.  I recommend doing 
performance tests from a real partition or volume.

-- 
error compiling committee.c: too many arguments to function


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Sun, 2007-07-08 at 11:14 +0300, Avi Kivity wrote:
> Dave Hansen wrote:
> > I've noticed that some of my tests run *MUCH* slower in kvm-28 than in
> > 27.  I'm sure that wall time is pretty wonky in the guests, but it is
> > much slower in real-world time as well.
> >
> > Here's a little test to create a 32MB zeroed file with dd.  Here it is
> > from kvm-27 (this took ~5.5 seconds on my wristwatch):
> > 33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec)
> > 33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec)
> >
> > Here's the same thing from kvm-28 (~80 seconds on my wristwatch):
> > 33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec)
> > 33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec)
> >
> > Same host kernel, same kvm kernel modules (from kvm-28) same guest
> > kernel, same command-line options, same disk image.
> >
> > Any ideas what is going on?
> >   
> 
> Is this repeatable?  I don't see anything in kvm-27..kvm-28 that 
> warrants such a regression.

Right now, it's completely repeatable

> Things to check:
> 
> - effect of pinning the vm onto one cpu (with 'taskset')

Tried this.  No effect that I can see at all.

> - does any counter in kvm_stat behave differently

Nothing really stands out.  The most strange thing to me is that the
counters are very stationary on the slow one.  It doesn't look like it
is spinning on something, just that it is idle.  Its counters during the
dd look very much like the guest does when it is idle:

the slow one:
dave@elm3b173:~$ KVM=28 HDA=qemu.raw ./run-qemu -snapshot
idle:
 efer_reload    156984     800
 exits          395676     800
 halt_exits       7165     100
 invlpg              0       0
 io_exits       123487     700
 irq_exits        1406       0
 irq_window        817       0
 light_exits    238692       0
 mmio_exits      24716       0
 pf_fixed       130354       0
 pf_guest        57309       0
 request_irq         0       0
 signal_exit       781       0
 tlb_flush        2267       0

dd'ing (mosly idle?):
 efer_reload    197669     856
 exits          455341     856
 halt_exits      11568     100
 invlpg              0       0
 io_exits       159006     740
 irq_exits        2125      14
 irq_window        975       2
 light_exits    257672       0
 mmio_exits      24716       0
 pf_fixed       146646       0
 pf_guest        59596       0
 request_irq         0       0
 signal_exit      1383      14
 tlb_flush        2455       0

burst during dd:
 efer_reload    205387     854
 exits          465166    2953
 halt_exits      12471      98
 invlpg              0       0
 io_exits       165605     733
 irq_exits        2341      30
 irq_window        985       2
 light_exits    259779    2099
 mmio_exits      24716       0
 pf_fixed       148731    2082
 pf_guest        59596       0
 request_irq         0       0
33554432 bytes transferred in 20.837575 seconds (1610285 bytes/sec)

the fast one:
$ KVM=27 HDA=qemu.raw ./run-qemu -snapshot
idle:
 efer_reload    164333     800
 exits          416798     800
 halt_exits       4570     100
 invlpg              0       0
 io_exits       132855     700
 irq_exits         838       0
 irq_window       2037       0
 light_exits    252465       0
 mmio_exits      24716       0
 pf_fixed       130325       0
 pf_guest        57275       0
 request_irq         0       0
 signal_exit       127       0
 tlb_flush        1864       0

during dd:
 efer_reload    243917   29963
 exits          523608   34205
 halt_exits       6766       0
 invlpg              0       0
 io_exits       207716   28730
 irq_exits        1079      52
 irq_window       4525    1232
 light_exits    279695    4235
 mmio_exits      24716       0
 pf_fixed       148656    4177
 pf_guest        59560       0
 request_irq         0       0
 signal_exit       154       7
 tlb_flush        2043       8
33554432 bytes transferred in 0.100797 seconds (332891147 bytes/sec)

> If you are using qcow, maybe the effect is due to the first test hitting 
> a hole and the second being forced to read from disk.  I recommend doing 
> performance tests from a real partition or volume.

I switched over to a raw image, and used -snapshot.  I don't have the
disk space to give them their own partitions right now.  

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Dave Hansen wrote:
> On Sun, 2007-07-08 at 11:14 +0300, Avi Kivity wrote:
>   
>> Dave Hansen wrote:
>>     
>>> I've noticed that some of my tests run *MUCH* slower in kvm-28 than in
>>> 27.  I'm sure that wall time is pretty wonky in the guests, but it is
>>> much slower in real-world time as well.
>>>
>>> Here's a little test to create a 32MB zeroed file with dd.  Here it is
>>> from kvm-27 (this took ~5.5 seconds on my wristwatch):
>>> 33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec)
>>> 33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec)
>>>
>>> Here's the same thing from kvm-28 (~80 seconds on my wristwatch):
>>> 33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec)
>>> 33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec)
>>>
>>> Same host kernel, same kvm kernel modules (from kvm-28) same guest
>>> kernel, same command-line options, same disk image.
>>>
>>> Any ideas what is going on?
>>>   
>>>       
>> Is this repeatable?  I don't see anything in kvm-27..kvm-28 that 
>> warrants such a regression.
>>     
>
> Right now, it's completely repeatable
>
>   
>> Things to check:
>>
>> - effect of pinning the vm onto one cpu (with 'taskset')
>>     
>
> Tried this.  No effect that I can see at all.
>
>   
>> - does any counter in kvm_stat behave differently
>>     
>
> Nothing really stands out.  The most strange thing to me is that the
> counters are very stationary on the slow one.  It doesn't look like it
> is spinning on something, just that it is idle.  Its counters during the
> dd look very much like the guest does when it is idle:
>   

What does 'top' on the host show in both cases?

There was a change in kvm userspace that affected IDE.  Can you try
kvm-27 userspace with a kvm-28 kernel module?  If that's slow, then the
only recourse is bisecting.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Tue, 2007-07-10 at 08:44 +0300, Avi Kivity wrote:
> What does 'top' on the host show in both cases?

On the fast one (kvm-27) I just see the dd as a flash in top.  It
doesn't stay for long.  The VM isn't very responsive during the dd.

On the slow (kvm-28) one, I see the dd in top creeping along, using ~2%
of the CPU.  The guest is responsive during this time

> There was a change in kvm userspace that affected IDE.  Can you try
> kvm-27 userspace with a kvm-28 kernel module?

That's actually what I've been doing the whole time.  Sorry, my initial
problem description must not have been very clear.  I've been using the
kvm-28 modules the entire time, and only varying the userspace.

The IDE changes do look suspect.

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Dave Hansen wrote:
> On Tue, 2007-07-10 at 08:44 +0300, Avi Kivity wrote:
>   
>> What does 'top' on the host show in both cases?
>>     
>
> On the fast one (kvm-27) I just see the dd as a flash in top.  It
> doesn't stay for long.  The VM isn't very responsive during the dd.
>
> On the slow (kvm-28) one, I see the dd in top creeping along, using ~2%
> of the CPU.  The guest is responsive during this time
>
>   
>> There was a change in kvm userspace that affected IDE.  Can you try
>> kvm-27 userspace with a kvm-28 kernel module?
>>     
>
> That's actually what I've been doing the whole time.  Sorry, my initial
> problem description must not have been very clear.  I've been using the
> kvm-28 modules the entire time, and only varying the userspace.
>
> The IDE changes do look suspect.
>
>   

Can you confirm it by backing out that one patch?

I don't see how it can cause this slowdown, except by causing a
different driver to be loaded or perhaps with different settings.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Thu, 2007-07-12 at 08:37 +0300, Avi Kivity wrote:
> Can you confirm it by backing out that one patch?

Do you know the git commit id by chance?

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Dave Hansen wrote:
> On Thu, 2007-07-12 at 08:37 +0300, Avi Kivity wrote:
>   
>> Can you confirm it by backing out that one patch?
>>     
>
> Do you know the git commit id by chance?
>
> -- Dave
>
>   
commit 55a3212bc2f5ecddcd4c5cdf2bfb37ad71e45ff2
Author: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Date:   Tue Jun 5 14:47:33 2007 +0300

    kvm: qemu: initialize ata ports as enabled

    this allows libata to see the qemu ata ports.

diff --git a/qemu/hw/ide.c b/qemu/hw/ide.c
index 190f074..ddfb9bc 100644
--- a/qemu/hw/ide.c
+++ b/qemu/hw/ide.c
@@ -2586,6 +2586,8 @@ static void piix3_reset(PCIIDEState *d)
     pci_conf[0x06] = 0x80; /* FBC */
     pci_conf[0x07] = 0x02; // PCI_status_devsel_medium
     pci_conf[0x20] = 0x01; /* BMIBA: 20-23h */
+    pci_conf[0x41] = 0x80; // enable port 0
+    pci_conf[0x43] = 0x80; // enable port 1
 }

 void pci_piix_ide_init(PCIBus *bus, BlockDriverState **hd_table, int devfn)


I was unable to reproduce this on a FC6 i386 guest.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/13/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
> Dave Hansen wrote:
> > On Thu, 2007-07-12 at 08:37 +0300, Avi Kivity wrote:
> >
> >> Can you confirm it by backing out that one patch?
> >>
> >
> > Do you know the git commit id by chance?
> >
> > -- Dave
> >
> >
> commit 55a3212bc2f5ecddcd4c5cdf2bfb37ad71e45ff2
> Author: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Date:   Tue Jun 5 14:47:33 2007 +0300
>
>     kvm: qemu: initialize ata ports as enabled
>
>     this allows libata to see the qemu ata ports.
>
> diff --git a/qemu/hw/ide.c b/qemu/hw/ide.c
> index 190f074..ddfb9bc 100644
> --- a/qemu/hw/ide.c
> +++ b/qemu/hw/ide.c
> @@ -2586,6 +2586,8 @@ static void piix3_reset(PCIIDEState *d)
>      pci_conf[0x06] = 0x80; /* FBC */
>      pci_conf[0x07] = 0x02; // PCI_status_devsel_medium
>      pci_conf[0x20] = 0x01; /* BMIBA: 20-23h */
> +    pci_conf[0x41] = 0x80; // enable port 0
> +    pci_conf[0x43] = 0x80; // enable port 1
>  }
>
>  void pci_piix_ide_init(PCIBus *bus, BlockDriverState **hd_table, int devfn)
>
>
> I was unable to reproduce this on a FC6 i386 guest.

Hum... I assume the FC6 is using the "old" IDE driver, yes? I can't
see why that patch should matter though... if those bits are not set
then the IDE controller is not decoding the commands (on real hw).

Luca

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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Luca wrote:
> On 7/13/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
>> Dave Hansen wrote:
>> > On Thu, 2007-07-12 at 08:37 +0300, Avi Kivity wrote:
>> >
>> >> Can you confirm it by backing out that one patch?
>> >>
>> >
>> > Do you know the git commit id by chance?
>> >
>> > -- Dave
>> >
>> >
>> commit 55a3212bc2f5ecddcd4c5cdf2bfb37ad71e45ff2
>> Author: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> Date:   Tue Jun 5 14:47:33 2007 +0300
>>
>>     kvm: qemu: initialize ata ports as enabled
>>
>>     this allows libata to see the qemu ata ports.
>>
>> diff --git a/qemu/hw/ide.c b/qemu/hw/ide.c
>> index 190f074..ddfb9bc 100644
>> --- a/qemu/hw/ide.c
>> +++ b/qemu/hw/ide.c
>> @@ -2586,6 +2586,8 @@ static void piix3_reset(PCIIDEState *d)
>>      pci_conf[0x06] = 0x80; /* FBC */
>>      pci_conf[0x07] = 0x02; // PCI_status_devsel_medium
>>      pci_conf[0x20] = 0x01; /* BMIBA: 20-23h */
>> +    pci_conf[0x41] = 0x80; // enable port 0
>> +    pci_conf[0x43] = 0x80; // enable port 1
>>  }
>>
>>  void pci_piix_ide_init(PCIBus *bus, BlockDriverState **hd_table, int
>> devfn)
>>
>>
>> I was unable to reproduce this on a FC6 i386 guest.
>
> Hum... I assume the FC6 is using the "old" IDE driver, yes? I can't
> see why that patch should matter though... if those bits are not set
> then the IDE controller is not decoding the commands (on real hw).
>

I tested FC6 i386 about found no difference with or without the patch.

Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace? 
Maybe that will tell us something.

-- 
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Re: kvm-27 vs 28 I/O speed

[Gregory Haskins]

On Fri, 2007-07-13 at 16:41 +0300, Avi Kivity wrote:


> I tested FC6 i386 about found no difference with or without the patch.
> 
> Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace? 
> Maybe that will tell us something.
> 

I can say this:  It would seem that the IDE enable bits "float" before
Lucas fix.  I say this because I had written/submitted a similar fix way
back in kvm-teens because I found that sometimes my SLED installer guest
would fail to see the IDE controller.  I found it to be that the IDE
controller wasn't enabled sometimes and setting the 0x80 bits as Luca
has done fixed the issue.

Then, I found that later versions of KVM (sans my patch) seemed to work
fine so I somewhat assumed the issue had been addressed.  When I saw
Lucas patch come through, I realized that it must not have been fixed,
but I was getting lucky that it tended to come up enabled pretty much
100%.

So heres what I think is happening:  I think that having the IDE
controller enabled is causing FC7 to go into a different mode of
operation, which is slower for whatever reason.  I think that Dave has a
system that relatively deterministically comes up disabled, and Avi has
one that comes up enabled.  Therefore, the patch has ill-effect for
Dave, and no-effect for Avi.

Therefore, to test this theory, Avi should modify Luca patch to
*disable* the IDE and see what happens.  If the theory is true, Avi will
see a speed improvement.

Just a shot in the dark... ;)

-Greg 


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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
> On Fri, 2007-07-13 at 16:41 +0300, Avi Kivity wrote:
>
>
> > I tested FC6 i386 about found no difference with or without the patch.
> >
> > Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace?
> > Maybe that will tell us something.
> >
>
> I can say this:  It would seem that the IDE enable bits "float" before
> Lucas fix.  I say this because I had written/submitted a similar fix way
> back in kvm-teens because I found that sometimes my SLED installer guest
> would fail to see the IDE controller.  I found it to be that the IDE
> controller wasn't enabled sometimes and setting the 0x80 bits as Luca
> has done fixed the issue.
>
> Then, I found that later versions of KVM (sans my patch) seemed to work
> fine so I somewhat assumed the issue had been addressed.  When I saw
> Lucas patch come through, I realized that it must not have been fixed,
> but I was getting lucky that it tended to come up enabled pretty much
> 100%.
>
> So heres what I think is happening:  I think that having the IDE
> controller enabled is causing FC7 to go into a different mode of
> operation, which is slower for whatever reason.  I think that Dave has a
> system that relatively deterministically comes up disabled, and Avi has
> one that comes up enabled.  Therefore, the patch has ill-effect for
> Dave, and no-effect for Avi.
>
> Therefore, to test this theory, Avi should modify Luca patch to
> *disable* the IDE and see what happens.  If the theory is true, Avi will
> see a speed improvement.
>
> Just a shot in the dark... ;)

Just to clarify: you are suggesting that the "old" IDE driver used to
see that the controller was disabled and reprogrammed it by itself
(fast mode); now it sees it's enabled and leaves whatever mode is
currently set.
I can't look at the sources right now but it's at least plausible ;-)

Luca

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Re: kvm-27 vs 28 I/O speed

[Gregory Haskins]

On Fri, 2007-07-13 at 16:46 +0200, Luca wrote:
> On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:

> Just to clarify: you are suggesting that the "old" IDE driver used to
> see that the controller was disabled and reprogrammed it by itself
> (fast mode); now it sees it's enabled and leaves whatever mode is
> currently set.
> I can't look at the sources right now but it's at least plausible ;-)
> 

Yeah.  As Im sure you are aware, those bits that your patch modifies are
(IIUC) for enabling/disabling access to the legacy IDE.  On real
hardware, they can be used by the bios to enable/disable the legacy IDE
function.  It doesnt actually disable the chip IIUC..its just a flag to
let higher layer software detect if the legacy IDE is usable.  In our
emulated environment, those bits were left undefined prior to your patch
(neither qemu nor bochs was configuring them).  Dont ask me why, but
what they initialized to was relatively consistent instead of random.
However, you cannot predict which way (on or off) and it seems each
environment was somewhat different (e.g. no one else was complaining
about the loss of IDE when i first stumbled on it, yet it was
consistently broken for me through a couple of releases).

So what I am thinking is that the drivers included with the FC7 kernel
are defaulting to some kind of slower legacy mode when they see it is
available and enabled.  Otherwise, they probably load some direct
non-legacy PCI driver and use that instead.

If this theory pans out, I would suggest we make some kind of flag in
qemu "--disable-legacy-ide" where the default is "enabled" (as your
patch does today).  That way, people with this issue can disable it in
the "bios" just like a real system.

-Greg



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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
> On Fri, 2007-07-13 at 16:46 +0200, Luca wrote:
> > On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
>
> > Just to clarify: you are suggesting that the "old" IDE driver used to
> > see that the controller was disabled and reprogrammed it by itself
> > (fast mode); now it sees it's enabled and leaves whatever mode is
> > currently set.
> > I can't look at the sources right now but it's at least plausible ;-)
> >
>
> Yeah.  As Im sure you are aware, those bits that your patch modifies are
> (IIUC) for enabling/disabling access to the legacy IDE.  On real
> hardware, they can be used by the bios to enable/disable the legacy IDE
> function.  It doesnt actually disable the chip IIUC..

Hum, are you *really* sure? Intel doc says:

"IDE Decode Enable (IDE). 1=Enable; 0=Disable. When enabled, I/O
transactions on PCI
targeting the IDE ATA register blocks (command block and control
block) are positively
decoded on PCI and driven on the IDE interface. When disabled, these
accesses are
subtractively decoded to ISA."

Now, "subtractively decoded to ISA" means that if nobody wants them
then those accesses are left to ISA devices (the PCI-to-ISA bridge
forwards them).
So IIRC setting the decode enable to 0 really means "disable the controller".

> its just a flag to let higher layer software detect if the legacy IDE is usable.  In our
> emulated environment, those bits were left undefined prior to your patch
> (neither qemu nor bochs was configuring them).

Bochs *is* enabling the ports; it's just that it does that in the
emulated device (i.e. the equivalent of out hw/ide.c) and not in the
BIOS.

Btw, the original thread is there:
http://thread.gmane.org/gmane.comp.emulators.kvm.devel/3619

> So what I am thinking is that the drivers included with the FC7 kernel
> are defaulting to some kind of slower legacy mode when they see it is
> available and enabled.  Otherwise, they probably load some direct
> non-legacy PCI driver and use that instead.

Nope, FC7 with libata doesn't find anything at all. It doesn't even
try to touch the controller if the ports are not enabled. This makes a
lot of sense since with ports disabled all the access to the command
and control blocks are forwarded to the ISA worlds (since the IDE
controller is not claiming the transactions).
I guess that the old driver has some logic like "BIOS is stupid, we
really want to enable this port".
Still, I fail to see why enabling the ports should reduce the speed.
Dave, can you confirm that backing out my patch fixes your speed issue?


Luca

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Re: kvm-27 vs 28 I/O speed

[Gregory Haskins]

On Fri, 2007-07-13 at 17:39 +0200, Luca wrote:
> On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
> > On Fri, 2007-07-13 at 16:46 +0200, Luca wrote:
> > > On 7/13/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
> >
> > > Just to clarify: you are suggesting that the "old" IDE driver used to
> > > see that the controller was disabled and reprogrammed it by itself
> > > (fast mode); now it sees it's enabled and leaves whatever mode is
> > > currently set.
> > > I can't look at the sources right now but it's at least plausible ;-)
> > >
> >
> > Yeah.  As Im sure you are aware, those bits that your patch modifies are
> > (IIUC) for enabling/disabling access to the legacy IDE.  On real
> > hardware, they can be used by the bios to enable/disable the legacy IDE
> > function.  It doesnt actually disable the chip IIUC..
> 
> Hum, are you *really* sure? Intel doc says:

Of course not!  That was a long time ago and my memory is fuzzy :P

> 
> "IDE Decode Enable (IDE). 1=Enable; 0=Disable. When enabled, I/O
> transactions on PCI
> targeting the IDE ATA register blocks (command block and control
> block) are positively
> decoded on PCI and driven on the IDE interface. When disabled, these
> accesses are
> subtractively decoded to ISA."
> 
> Now, "subtractively decoded to ISA" means that if nobody wants them
> then those accesses are left to ISA devices (the PCI-to-ISA bridge
> forwards them).
> So IIRC setting the decode enable to 0 really means "disable the controller".


I think what you say is 100% accurate, but you are taking what I was
saying too literally.  All I meant was that I don't think setting those
bits to enabled/disabled actually affects whether the IDE subsystem can
still be *used* or not...but rather it affects the interface that can be
used to access them.  

I could very well be totally wrong here, but the way I see it is that
some of these chips like the ICH present multiple abstractions to a
single subsystem.  I.e. there might be ISA representation for a feature
X, as well as a PCI representation.  Both of these features end up at
the same "IDE ribbon cable" so to speak, but the logical controller
abstraction is overloaded on multiple interfaces (e.g. ISA and PCI) and
can be independently manipulated.

Those bits in question enable the presentation of the standard IDE
interfaces.  However, IIRC there are ways to access the ide without
using the legacy IDE command/control blocks (e.g. via a PIIX3 mass
storage controller in PCI space).
  
> 
> > its just a flag to let higher layer software detect if the legacy IDE is usable.  In our
> > emulated environment, those bits were left undefined prior to your patch
> > (neither qemu nor bochs was configuring them).
> 
> Bochs *is* enabling the ports; it's just that it does that in the
> emulated device (i.e. the equivalent of out hw/ide.c) and not in the
> BIOS.

I don't doubt you, but that is contrary to the observed behavior I saw.
My SLED installed kept telling me I didnt have a valid hard-disk.
Debugging, I found that the IDE subsystem was skipping the disks because
they were disabled in bios..leading me to make a similar patch as yours
which fixed the problem.  If bochs was setting those bits, they were
gone by the time the installer got to them ;)

> 
> Btw, the original thread is there:
> http://thread.gmane.org/gmane.comp.emulators.kvm.devel/3619
> 
> > So what I am thinking is that the drivers included with the FC7 kernel
> > are defaulting to some kind of slower legacy mode when they see it is
> > available and enabled.  Otherwise, they probably load some direct
> > non-legacy PCI driver and use that instead.
> 
> Nope, FC7 with libata doesn't find anything at all. It doesn't even
> try to touch the controller if the ports are not enabled. This makes a
> lot of sense since with ports disabled all the access to the command
> and control blocks are forwarded to the ISA worlds (since the IDE
> controller is not claiming the transactions).
> I guess that the old driver has some logic like "BIOS is stupid, we
> really want to enable this port".
> Still, I fail to see why enabling the ports should reduce the speed.
> Dave, can you confirm that backing out my patch fixes your speed issue?

I don't think this is what is happening.  I think what happens is the
legacy IDE driver tries its probe and fails due to the disabled bits.
Later a different driver succeeds at its probe (e.g. say a PCI based
PIIX3 or similar).  Likewise, I am guessing that this other driver is
more efficient at virtualization due to its interaction with the device.
But, like I mentioned, I am guessing here. ;)



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Re: kvm-27 vs 28 I/O speed

[Gregory Haskins]

On Fri, 2007-07-13 at 17:39 +0200, Luca wrote:

> Still, I fail to see why enabling the ports should reduce the speed.
> Dave, can you confirm that backing out my patch fixes your speed issue?

BTW: I said what I said because I thought people had already bisected
the problem down to your patch.  If that's not the case, then what I
said is probably completely invalid, and I apologize for wasting
everyone's time.


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Fri, 2007-07-13 at 16:41 +0300, Avi Kivity wrote:
> I tested FC6 i386 about found no difference with or without the patch.

I've git bisected down the the same patch that you pasted above.  I've
also tried just applying that single patch to kvm-27 and reproduced the
slow behavior.

> Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace? 
> Maybe that will tell us something.

Here's kvm-27 and kvm-27+55a3212bc2...:


diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt 

 Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
 BIOS-provided physical RAM map:
@@ -39,7 +22,7 @@
 Enabling unmasked SIMD FPU exception support... done.
 Initializing CPU#0
 PID hash table entries: 512 (order: 9, 2048 bytes)
-Detected 2669.668 MHz processor.
+Detected 2669.011 MHz processor.
 Console: colour VGA+ 80x25
 Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
 Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
@@ -53,7 +36,7 @@
       .data : 0xc036efcf - 0xc043911c   ( 808 kB)
       .text : 0xc0100000 - 0xc036efcf   (2491 kB)
 Checking if this processor honours the WP bit even in supervisor mode... Ok.
-Calibrating delay using timer specific routine.. 26758.82 BogoMIPS (lpj=53517640)
+Calibrating delay using timer specific routine.. 26800.00 BogoMIPS (lpj=53600004)
 Mount-cache hash table entries: 512
 CPU: L1 I cache: 8K
 CPU: L2 cache: 128K
@@ -107,20 +90,21 @@
 PIIX3: IDE controller at PCI slot 0000:00:01.1
 PIIX3: chipset revision 0
 PIIX3: not 100% native mode: will probe irqs later
-PIIX3: neither IDE port enabled (BIOS)
+    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
+    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
 hda: QEMU HARDDISK, ATA DISK drive
 hdb: QEMU HARDDISK, ATA DISK drive
-Clocksource tsc unstable (delta = 767711774 ns)
+ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
+Clocksource tsc unstable (delta = 768021683 ns)
 Time: pit clocksource has been installed.
 hdc: QEMU CD-ROM, ATAPI CD/DVD-ROM drive
-ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
 ide1 at 0x170-0x177,0x376 on irq 15
 hda: max request size: 512KiB
-hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63
+hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63, (U)DMA
 hda: cache flushes supported
  hda: hda1
 hdb: max request size: 512KiB
-hdb: 262144 sectors (134 MB) w/256KiB Cache, CHS=260/255/63
+hdb: 262144 sectors (134 MB) w/256KiB Cache, CHS=260/255/63, (U)DMA
 hdb: cache flushes supported
  hdb: hdb1
 serio: i8042 KBD port at 0x60,0x64 irq 1
@@ -146,7 +130,7 @@
 Adding 128480k swap on /dev/hdb1.  Priority:-1 extents:1 across:128480k
 Checking root file system...
 fsck 1.37 (21-Mar-2005)
-/dev/hda1: clean, 46970/655360 files, 287821/1309289 blocks
+/dev/hda1: clean, 46970/655360 files, 287829/1309289 blocks
 EXT3 FS on hda1, internal journal
 Cleaning up ifupdown...done.
 Checking all file systems...

Looks like the slow versions have DMA enabled.  Is it slower to emulate
DMA than PIO?

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Fri, 2007-07-13 at 17:39 +0200, Luca wrote:
> Dave, can you confirm that backing out my patch fixes your speed
> issue? 

Sure, I'll check current git with and without your patch.

I've reproduced that _applying_ it to kvm-27 creates the slowdown, but
I'll double-check that backing it out restores things.

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Anthony Liguori]

Dave Hansen wrote:
> On Fri, 2007-07-13 at 16:41 +0300, Avi Kivity wrote:
>   
>> I tested FC6 i386 about found no difference with or without the patch.
>>     
>
> I've git bisected down the the same patch that you pasted above.  I've
> also tried just applying that single patch to kvm-27 and reproduced the
> slow behavior.
>
>   
>> Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace? 
>> Maybe that will tell us something.
>>     
>
> Here's kvm-27 and kvm-27+55a3212bc2...:
>
>
> diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt 
>
>  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
>  BIOS-provided physical RAM map:
> @@ -39,7 +22,7 @@
>  Enabling unmasked SIMD FPU exception support... done.
>  Initializing CPU#0
>  PID hash table entries: 512 (order: 9, 2048 bytes)
> -Detected 2669.668 MHz processor.
> +Detected 2669.011 MHz processor.
>  Console: colour VGA+ 80x25
>  Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
>  Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
> @@ -53,7 +36,7 @@
>        .data : 0xc036efcf - 0xc043911c   ( 808 kB)
>        .text : 0xc0100000 - 0xc036efcf   (2491 kB)
>  Checking if this processor honours the WP bit even in supervisor mode... Ok.
> -Calibrating delay using timer specific routine.. 26758.82 BogoMIPS (lpj=53517640)
> +Calibrating delay using timer specific routine.. 26800.00 BogoMIPS (lpj=53600004)
>  Mount-cache hash table entries: 512
>  CPU: L1 I cache: 8K
>  CPU: L2 cache: 128K
> @@ -107,20 +90,21 @@
>  PIIX3: IDE controller at PCI slot 0000:00:01.1
>  PIIX3: chipset revision 0
>  PIIX3: not 100% native mode: will probe irqs later
> -PIIX3: neither IDE port enabled (BIOS)
> +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
>   

There's your problem.  With that patch, your kernel is using PIO instead 
of DMA.

I'm not 100% sure what's going here other than the fact that this 
particular problem has cropped up a number of times on qemu-devel.  It's 
been very difficult to get all guests to actually use DMA.

Regards,

Anthony Liguori

>  hda: QEMU HARDDISK, ATA DISK drive
>  hdb: QEMU HARDDISK, ATA DISK drive
> -Clocksource tsc unstable (delta = 767711774 ns)
> +ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
> +Clocksource tsc unstable (delta = 768021683 ns)
>  Time: pit clocksource has been installed.
>  hdc: QEMU CD-ROM, ATAPI CD/DVD-ROM drive
> -ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
>  ide1 at 0x170-0x177,0x376 on irq 15
>  hda: max request size: 512KiB
> -hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63
> +hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63, (U)DMA
>  hda: cache flushes supported
>   hda: hda1
>  hdb: max request size: 512KiB
> -hdb: 262144 sectors (134 MB) w/256KiB Cache, CHS=260/255/63
> +hdb: 262144 sectors (134 MB) w/256KiB Cache, CHS=260/255/63, (U)DMA
>  hdb: cache flushes supported
>   hdb: hdb1
>  serio: i8042 KBD port at 0x60,0x64 irq 1
> @@ -146,7 +130,7 @@
>  Adding 128480k swap on /dev/hdb1.  Priority:-1 extents:1 across:128480k
>  Checking root file system...
>  fsck 1.37 (21-Mar-2005)
> -/dev/hda1: clean, 46970/655360 files, 287821/1309289 blocks
> +/dev/hda1: clean, 46970/655360 files, 287829/1309289 blocks
>  EXT3 FS on hda1, internal journal
>  Cleaning up ifupdown...done.
>  Checking all file systems...
>
> Looks like the slow versions have DMA enabled.  Is it slower to emulate
> DMA than PIO?
>
> -- Dave
>
>
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>   


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Anthony Liguori wrote:
>>  
>>> Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace?
>>> Maybe that will tell us something.
>>>     
>>
>> Here's kvm-27 and kvm-27+55a3212bc2...:
>>
>>
>> diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
>>  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu
>> 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
>>  BIOS-provided physical RAM map:
>> @@ -107,20 +90,21 @@
>>  PIIX3: IDE controller at PCI slot 0000:00:01.1
>>  PIIX3: chipset revision 0
>>  PIIX3: not 100% native mode: will probe irqs later
>> -PIIX3: neither IDE port enabled (BIOS)
>> +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
>> +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
>>   
>
> There's your problem.  With that patch, your kernel is using PIO
> instead of DMA.
>

Yeah, but later:

>>
>>  hda: max request size: 512KiB
>> -hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63
>> +hda: 10485760 sectors (5368 MB) w/256KiB Cache, CHS=10402/255/63,
>> (U)DMA
>>  hda: cache flushes supported
>>   
>

So now the slow version uses dma.

My attempt at wild guessing is that if the port is disabled, Linux
enables it and configures it correctly.  If it is already enabled, Linux
trusts the bios to have configured it and leaves it at some silly default.

Dave, can you compare the output of hdparm -v /dev/hda?  Maybe more
clues there.


My FC6 i386 guest says:

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    = 256 (on)
 geometry     = 16383/255/63, sectors = 20971520, start = 0

Which seems nice and sane.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/13/07, Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org> wrote:
> Dave Hansen wrote:
> > On Fri, 2007-07-13 at 16:41 +0300, Avi Kivity wrote:
> >
> >> I tested FC6 i386 about found no difference with or without the patch.
> >>
> >
> > I've git bisected down the the same patch that you pasted above.  I've
> > also tried just applying that single patch to kvm-27 and reproduced the
> > slow behavior.
> >
> >
> >> Dave, can you diff the guest dmesg with kvm-27 and kvm-28 userspace?
> >> Maybe that will tell us something.
> >>
> >
> > Here's kvm-27 and kvm-27+55a3212bc2...:
> >
> >
> > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> >
> >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
> >  BIOS-provided physical RAM map:
> > @@ -39,7 +22,7 @@
> >  Enabling unmasked SIMD FPU exception support... done.
> >  Initializing CPU#0
> >  PID hash table entries: 512 (order: 9, 2048 bytes)
> > -Detected 2669.668 MHz processor.
> > +Detected 2669.011 MHz processor.
> >  Console: colour VGA+ 80x25
> >  Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
> >  Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
> > @@ -53,7 +36,7 @@
> >        .data : 0xc036efcf - 0xc043911c   ( 808 kB)
> >        .text : 0xc0100000 - 0xc036efcf   (2491 kB)
> >  Checking if this processor honours the WP bit even in supervisor mode... Ok.
> > -Calibrating delay using timer specific routine.. 26758.82 BogoMIPS (lpj=53517640)
> > +Calibrating delay using timer specific routine.. 26800.00 BogoMIPS (lpj=53600004)
> >  Mount-cache hash table entries: 512
> >  CPU: L1 I cache: 8K
> >  CPU: L2 cache: 128K
> > @@ -107,20 +90,21 @@
> >  PIIX3: IDE controller at PCI slot 0000:00:01.1
> >  PIIX3: chipset revision 0
> >  PIIX3: not 100% native mode: will probe irqs later
> > -PIIX3: neither IDE port enabled (BIOS)
> > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
> >
>
> There's your problem.  With that patch, your kernel is using PIO instead
> of DMA.
>
> I'm not 100% sure what's going here other than the fact that this
> particular problem has cropped up a number of times on qemu-devel.  It's
> been very difficult to get all guests to actually use DMA.

Those are the BIOS settings, which are consistent with what QEMU is
doing. Linux driver is actually configuring the device for MWDMA2

Luca

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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
>
>  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007

Is this a vanilla 2.6.22? 32 bit?

> @@ -107,20 +90,21 @@
>  PIIX3: IDE controller at PCI slot 0000:00:01.1
>  PIIX3: chipset revision 0
>  PIIX3: not 100% native mode: will probe irqs later
> -PIIX3: neither IDE port enabled (BIOS)
> +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio

Hum, FC6 PIIX driver always comes up with the same mode, regardless of
what I'm doing to the controller...

Luca

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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> >
> >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
>
> Is this a vanilla 2.6.22? 32 bit?
>
> > @@ -107,20 +90,21 @@
> >  PIIX3: IDE controller at PCI slot 0000:00:01.1
> >  PIIX3: chipset revision 0
> >  PIIX3: not 100% native mode: will probe irqs later
> > -PIIX3: neither IDE port enabled (BIOS)
> > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
>
> Hum, FC6 PIIX driver always comes up with the same mode, regardless of
> what I'm doing to the controller...

Ok, now I'm confused...

pci_config_write: PIIX3 IDE: addr=40 val=00008000 len=2
pci_config_write: PIIX3 IDE: addr=42 val=00008000 len=2

I'm using KVM-27 userspace, and the BIOS is enabling both ports. So...
linux shouldn't think that the ports are disabled (yet I saw the same
thing with FC7 and libata).

Luca

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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> > > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> > >
> > >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
> >
> > Is this a vanilla 2.6.22? 32 bit?
> >
> > > @@ -107,20 +90,21 @@
> > >  PIIX3: IDE controller at PCI slot 0000:00:01.1
> > >  PIIX3: chipset revision 0
> > >  PIIX3: not 100% native mode: will probe irqs later
> > > -PIIX3: neither IDE port enabled (BIOS)
> > > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> > > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
> >
> > Hum, FC6 PIIX driver always comes up with the same mode, regardless of
> > what I'm doing to the controller...
>
> Ok, now I'm confused...
>
> pci_config_write: PIIX3 IDE: addr=40 val=00008000 len=2
> pci_config_write: PIIX3 IDE: addr=42 val=00008000 len=2
>
> I'm using KVM-27 userspace, and the BIOS is enabling both ports. So...
> linux shouldn't think that the ports are disabled (yet I saw the same
> thing with FC7 and libata).

Oh fuck, it's obvious... If you don't supply -L on the command line
KVM ends up using the BIOS in the default system directory
(/usr/share{,local}/qemu); on my system this the BIOS installed by
QEMU 0.9, which does *not* enable the IDE ports. OTOH the BIOS file
shipped with KVM does enable the ports.
I guess that you're seeing the same thing: you used to run KVM+QEMU
bios (ports disabled - fast); then KVM started to enable IDE ports
(even with QEMU bios) and you saw a regression.
Can you re-test KVM 27 with it's BIOS (i.e. use something like -L
~/src/kvm-27/qemu/pc-bios)?

FYI I'm seeing a better tput with MWDMA2 (ports enabled) rather than
with PIO (ports disabled).

Luca

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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Luca wrote:
> On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> > On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
>> > > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
>> > >
>> > >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 
>> 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
>> >
>> > Is this a vanilla 2.6.22? 32 bit?
>> >
>> > > @@ -107,20 +90,21 @@
>> > >  PIIX3: IDE controller at PCI slot 0000:00:01.1
>> > >  PIIX3: chipset revision 0
>> > >  PIIX3: not 100% native mode: will probe irqs later
>> > > -PIIX3: neither IDE port enabled (BIOS)
>> > > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
>> > > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
>> >
>> > Hum, FC6 PIIX driver always comes up with the same mode, regardless of
>> > what I'm doing to the controller...
>>
>> Ok, now I'm confused...
>>
>> pci_config_write: PIIX3 IDE: addr=40 val=00008000 len=2
>> pci_config_write: PIIX3 IDE: addr=42 val=00008000 len=2
>>
>> I'm using KVM-27 userspace, and the BIOS is enabling both ports. So...
>> linux shouldn't think that the ports are disabled (yet I saw the same
>> thing with FC7 and libata).
>
> Oh fuck, it's obvious... If you don't supply -L on the command line
> KVM ends up using the BIOS in the default system directory
> (/usr/share{,local}/qemu); on my system this the BIOS installed by
> QEMU 0.9, which does *not* enable the IDE ports. OTOH the BIOS file
> shipped with KVM does enable the ports.
> I guess that you're seeing the same thing: you used to run KVM+QEMU
> bios (ports disabled - fast); then KVM started to enable IDE ports
> (even with QEMU bios) and you saw a regression.
> Can you re-test KVM 27 with it's BIOS (i.e. use something like -L
> ~/src/kvm-27/qemu/pc-bios)?
>
> FYI I'm seeing a better tput with MWDMA2 (ports enabled) rather than
> with PIO (ports disabled).

So, would it be correct to revert the patch enabling the ports, assuming 
people use the kvm-supplied bios?


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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/16/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
> Luca wrote:
> > On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> On 7/15/07, Luca <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> > On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> >> > > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> >> > >
> >> > >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu
> >> 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
> >> >
> >> > Is this a vanilla 2.6.22? 32 bit?
> >> >
> >> > > @@ -107,20 +90,21 @@
> >> > >  PIIX3: IDE controller at PCI slot 0000:00:01.1
> >> > >  PIIX3: chipset revision 0
> >> > >  PIIX3: not 100% native mode: will probe irqs later
> >> > > -PIIX3: neither IDE port enabled (BIOS)
> >> > > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> >> > > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
> >> >
> >> > Hum, FC6 PIIX driver always comes up with the same mode, regardless of
> >> > what I'm doing to the controller...
> >>
> >> Ok, now I'm confused...
> >>
> >> pci_config_write: PIIX3 IDE: addr=40 val=00008000 len=2
> >> pci_config_write: PIIX3 IDE: addr=42 val=00008000 len=2
> >>
> >> I'm using KVM-27 userspace, and the BIOS is enabling both ports. So...
> >> linux shouldn't think that the ports are disabled (yet I saw the same
> >> thing with FC7 and libata).
> >
> > Oh fuck, it's obvious... If you don't supply -L on the command line
> > KVM ends up using the BIOS in the default system directory
> > (/usr/share{,local}/qemu); on my system this the BIOS installed by
> > QEMU 0.9, which does *not* enable the IDE ports. OTOH the BIOS file
> > shipped with KVM does enable the ports.
> > I guess that you're seeing the same thing: you used to run KVM+QEMU
> > bios (ports disabled - fast); then KVM started to enable IDE ports
> > (even with QEMU bios) and you saw a regression.
> > Can you re-test KVM 27 with it's BIOS (i.e. use something like -L
> > ~/src/kvm-27/qemu/pc-bios)?
> >
> > FYI I'm seeing a better tput with MWDMA2 (ports enabled) rather than
> > with PIO (ports disabled).
>
> So, would it be correct to revert the patch enabling the ports, assuming
> people use the kvm-supplied bios?

I think so. Where does the BIOS come from? Latest Bochs?

Luca

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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Sat, 2007-07-14 at 09:27 +0300, Avi Kivity wrote:
> Dave, can you compare the output of hdparm -v /dev/hda?  Maybe more
> clues there.

slow:
qemu:~# hdparm -v /dev/hda

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    = 256 (on)
 geometry     = 10402/255/63, sectors = 10485760, start = 0


fast:
qemu:~# hdparm -v /dev/hda

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  0 (off)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    = 256 (on)
 geometry     = 10402/255/63, sectors = 10485760, start = 0


-- Dave


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Sun, 2007-07-15 at 21:27 +0200, Luca wrote:
> On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> >
> >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
> 
> Is this a vanilla 2.6.22? 32 bit?

Yep, vanilla.

> > @@ -107,20 +90,21 @@
> >  PIIX3: IDE controller at PCI slot 0000:00:01.1
> >  PIIX3: chipset revision 0
> >  PIIX3: not 100% native mode: will probe irqs later
> > -PIIX3: neither IDE port enabled (BIOS)
> > +    ide0: BM-DMA at 0x1400-0x1407, BIOS settings: hda:pio, hdb:pio
> > +    ide1: BM-DMA at 0x1408-0x140f, BIOS settings: hdc:pio, hdd:pio
> 
> Hum, FC6 PIIX driver always comes up with the same mode, regardless of
> what I'm doing to the controller...


-- Dave


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Sun, 2007-07-15 at 21:27 +0200, Luca wrote:
> On 7/13/07, Dave Hansen <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> > diff -ru kvm-fast-dmesg.txt kvm-slow-dmesg.txt
> >
> >  Linux version 2.6.22 (dave@kernel) (gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)) #13 Wed Jul 11 15:27:01 PDT 2007
> 
> Is this a vanilla 2.6.22? 32 bit?

And, yes 32-bit kernel.  But, I'm running it on the x86_64 version kvm
on an x86_64 host.

-- Dave


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Re: kvm-27 vs 28 I/O speed

[Dave Hansen]

On Sun, 2007-07-15 at 23:22 +0200, Luca wrote:
> Can you re-test KVM 27 with it's BIOS (i.e. use something like -L
> ~/src/kvm-27/qemu/pc-bios)? 

Doing that does appear to make it behave like kvm-28.  DMA enabled, and
slow I/O:

qemu:~# hdparm -v /dev/hda

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  0 (default 16-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    = 256 (on)
 geometry     = 10402/255/63, sectors = 10485760, start = 0


-- Dave


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Re: kvm-27 vs 28 I/O speed

[Avi Kivity]

Luca wrote:
>>
>> So, would it be correct to revert the patch enabling the ports, assuming
>> people use the kvm-supplied bios?
>
> I think so. 

Please confirm that the original test case (I think it was the FC7 
installer?) works with the kvm bios.

> Where does the BIOS come from? Latest Bochs?
>

Yes.  See qemu/pc-bios/bochs-manifest.


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Re: kvm-27 vs 28 I/O speed

[Luca]

On 7/17/07, Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
> Luca wrote:
> >>
> >> So, would it be correct to revert the patch enabling the ports, assuming
> >> people use the kvm-supplied bios?
> >
> > I think so.
>
> Please confirm that the original test case (I think it was the FC7
> installer?) works with the kvm bios.

Yes, FC7 libata driver does see the disks.

Luca

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