Re: kvm-27 vs 28 I/O speed

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

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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