RE: does cpu_idle() halt CPU?

RE: does cpu_idle() halt CPU?

[Grover, Andrew]

> From: Jun Sun [mailto:jsun-vWJf10E4RRusTnJN9+BGXg@public.gmane.org] 

> [root@localhost root]# cat /proc/acpi/processor/CPU0/power
> active state:            C2
> default state:           C1
> bus master activity:     ffffffff
> states:
>     C1:                  promotion[C2] demotion[--] 
> latency[000] usage[00000690]   *C2:                  
> promotion[C3] demotion[C1] latency[010] usage[00196669]    
> C3:                  promotion[--] demotion[C2] latency[130] 
> usage[00000000]

Your system either doesn't support C3, or the constant bus master
activity is keeping it out of C3. USB can cause this, but also AC97.

> > - What does the ACPI: Processor line say in your dmesg say?

There should be a line that says, "ACPI: Processor found (x perf states
y throttle)" Is that there? It may be occurring later on in the boot
process.

> > What kind of laptop do you have? Does it support SpeedStep, 
> PowerNow, or
> > the like?
> 
> My laptop is Fujitsu S6110.  CPU supports speedstep.

Getting into the lowest SpeedStep state will help battery life. You may
want to investigate the cpufreq project.

Regards -- Andy


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Re: does cpu_idle() halt CPU?

[Jun Sun]

On Fri, Mar 28, 2003 at 02:43:32PM -0800, Grover, Andrew wrote:
> 
> Your system either doesn't support C3, or the constant bus master
> activity is keeping it out of C3. USB can cause this, but also AC97.
>

No USB and AC97.  Have 802.11 card working.  Not sure if this matters.

 
> > > - What does the ACPI: Processor line say in your dmesg say?
> 
> There should be a line that says, "ACPI: Processor found (x perf states
> y throttle)" Is that there? It may be occurring later on in the boot
> process.
>

I found this line:
 
ACPI: Processor [CPU0] (supports C1 C2 C3, 2 performance states)

> > > What kind of laptop do you have? Does it support SpeedStep, 
> > PowerNow, or
> > > the like?
> > 
> > My laptop is Fujitsu S6110.  CPU supports speedstep.
> 
> Getting into the lowest SpeedStep state will help battery life. You may
> want to investigate the cpufreq project.
> 

So my previous conclusion about C1/C2 not saving power is right?

Thanks a lot.

Jun


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Re: does cpu_idle() halt CPU?

[Ducrot Bruno]

On Fri, Mar 28, 2003 at 03:02:18PM -0800, Jun Sun wrote:
> On Fri, Mar 28, 2003 at 02:43:32PM -0800, Grover, Andrew wrote:
> > 
> > Your system either doesn't support C3, or the constant bus master
> > activity is keeping it out of C3. USB can cause this, but also AC97.
> >
> 
> No USB and AC97.  Have 802.11 card working.  Not sure if this matters.

Who knows..

> 
>  
> > > > - What does the ACPI: Processor line say in your dmesg say?
> > 
> > There should be a line that says, "ACPI: Processor found (x perf states
> > y throttle)" Is that there? It may be occurring later on in the boot
> > process.
> >
> 
> I found this line:
>  
> ACPI: Processor [CPU0] (supports C1 C2 C3, 2 performance states)
> 
> > > > What kind of laptop do you have? Does it support SpeedStep, 
> > > PowerNow, or
> > > > the like?
> > > 
> > > My laptop is Fujitsu S6110.  CPU supports speedstep.
> > 
> > Getting into the lowest SpeedStep state will help battery life. You may
> > want to investigate the cpufreq project.
> > 
> 
> So my previous conclusion about C1/C2 not saving power is right?
> 

No.  C2 will give you some power saving (try to disable explicitely and
you will see a decrease of the battery life).

You forgot at least disk activities especially if ext3, which
prevent almost all IDE drivers to go to idle state.
But that will not explain why you can not go to C3 though.

Cheers,

-- 
Ducrot Bruno

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.


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Re: does cpu_idle() halt CPU?

[Jan Rychter]

>>>>> "DB" == Ducrot Bruno <ducrot-kk6yZipjEM5g9hUCZPvPmw@public.gmane.org>:
[...]
 DB> You forgot at least disk activities especially if ext3, which
 DB> prevent almost all IDE drivers to go to idle state.  But that will
 DB> not explain why you can not go to C3 though.

By the way, let me ask here: does anybody know what would be the best
filesystem to use on a laptop, power saving being the #1 priority? Are
all journaling filesystems this bad?

There was a project to teach the Linux kernel about drive spindown and
manage drive accesses accordingly -- but last time I saw their docs they
said that all journaling filesystems pose serious problems...

USB preventing the machine from going into C3 is a serious problem. I
still don't understand if that's a hardware thing or can we have a more
reasonable HCI implementation that doesn't use DMA that much. How does
Windows deal with it?

--J.


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Re: Re: does cpu_idle() halt CPU?

[Matthew Keller]

SGI's XFS is wonderful, AFAICT. Just make sure you have the latest tools
and whatnot.

On Wed, 2003-04-02 at 02:05, Jan Rychter wrote:
> >>>>> "DB" == Ducrot Bruno <ducrot-kk6yZipjEM5g9hUCZPvPmw@public.gmane.org>:
> [...]
>  DB> You forgot at least disk activities especially if ext3, which
>  DB> prevent almost all IDE drivers to go to idle state.  But that will
>  DB> not explain why you can not go to C3 though.
> 
> By the way, let me ask here: does anybody know what would be the best
> filesystem to use on a laptop, power saving being the #1 priority? Are
> all journaling filesystems this bad?
> 
> There was a project to teach the Linux kernel about drive spindown and
> manage drive accesses accordingly -- but last time I saw their docs they
> said that all journaling filesystems pose serious problems...
> 
> USB preventing the machine from going into C3 is a serious problem. I
> still don't understand if that's a hardware thing or can we have a more
> reasonable HCI implementation that doesn't use DMA that much. How does
> Windows deal with it?
> 
> --J.
> 
> 
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-- 
Matthew Keller
Enterprise Systems Analyst
Computing & Technology Services
State University of New York @ Potsdam
Potsdam, NY USA
http://mattwork.potsdam.edu/



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Re: Re: does cpu_idle() halt CPU?

[Karol Kozimor]

Thus wrote Matthew Keller:
> SGI's XFS is wonderful, AFAICT. Just make sure you have the latest tools
> and whatnot.

Are you sure? I am using XFS on both my partitions, both mounted with
noatime, I told syslog not to sync upon write, yet the disk still keeps
spinning up arbitrarily (usually after 30 - 90 seconds). Or perhaps the
cause lies somewhere else?
Best regards,

-- 
Karol 'sziwan' Kozimor
sziwan-DETuoxkZsSqrDJvtcaxF/A@public.gmane.org


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Re: Re: does cpu_idle() halt CPU?

[Matthew Keller]

On Thu, 2003-04-03 at 01:47, Karol Kozimor wrote:
> Thus wrote Matthew Keller:
> > SGI's XFS is wonderful, AFAICT. Just make sure you have the latest tools
> > and whatnot.
> 
> Are you sure? I am using XFS on both my partitions, both mounted with
> noatime, I told syslog not to sync upon write, yet the disk still keeps
> spinning up arbitrarily (usually after 30 - 90 seconds). Or perhaps the
> cause lies somewhere else?
> Best regards,

I've got 4 partitions (root, /usr, /home and /var/log) and everything is
copacetic. One thing to note is that I, uh, don't use syslog on my
laptop as disabling it saves my battery life by 10-15%. Try disabling it
and seeing where that leads, perhaps?

-- 
Matthew Keller
Enterprise Systems Analyst
Computing & Technology Services
State University of New York @ Potsdam
Potsdam, NY USA
http://mattwork.potsdam.edu/



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Re: does cpu_idle() halt CPU?

[Jan Rychter]

>>>>> "Matthew" == Matthew Keller <kellermg-aGob3lNJgTKVc3sceRu5cw@public.gmane.org>:
 Matthew> On Thu, 2003-04-03 at 01:47, Karol Kozimor wrote:
 >> Thus wrote Matthew Keller:
 > SGI's XFS is wonderful, AFAICT. Just make sure you have the latest
 > tools and whatnot.
 >>
 >> Are you sure? I am using XFS on both my partitions, both mounted
 >> with noatime, I told syslog not to sync upon write, yet the disk
 >> still keeps spinning up arbitrarily (usually after 30 - 90
 >> seconds). Or perhaps the cause lies somewhere else?  Best regards,

 Matthew> I've got 4 partitions (root, /usr, /home and /var/log) and
 Matthew> everything is copacetic. One thing to note is that I, uh,
 Matthew> don't use syslog on my laptop as disabling it saves my battery
 Matthew> life by 10-15%. Try disabling it and seeing where that leads,
 Matthew> perhaps?

noflushd (http://noflushd.sourceforge.net/ is what I was talking about
when I mentioned a project to hold disk writes when the disk is spun
down.

Unfortunately, the project info page says it doesn't help with
reiserfs. It also seems to be stagnant (but perhaps it just works so
well?).

--J.


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Re: Re: does cpu_idle() halt CPU?

[Charl P. Botha]

On Wed, Apr 02, 2003 at 09:05:06AM +0200, Jan Rychter wrote:
> >>>>> "DB" == Ducrot Bruno <ducrot-kk6yZipjEM5g9hUCZPvPmw@public.gmane.org>:
> [...]
>  DB> You forgot at least disk activities especially if ext3, which
>  DB> prevent almost all IDE drivers to go to idle state.  But that will
>  DB> not explain why you can not go to C3 though.
> 
> By the way, let me ask here: does anybody know what would be the best
> filesystem to use on a laptop, power saving being the #1 priority? Are
> all journaling filesystems this bad?

I'm having great results with ext3 by making sure that all my filesystems
are mounted with the noatime option.

-- 
charl p. botha http://cpbotha.net/ http://visualisation.tudelft.nl/


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RE: Re: does cpu_idle() halt CPU?

[Grover, Andrew]

> From: Jan Rychter [mailto:jan-JAsPCFd0eodBDgjK7y7TUQ@public.gmane.org] 
> USB preventing the machine from going into C3 is a serious 
> problem. I still don't understand if that's a hardware thing 
> or can we have a more reasonable HCI implementation that 
> doesn't use DMA that much. How does Windows deal with it?

Busmaster PCI devices keep us from using C3, because the CPU needs to be
in C2 or higher to handle bus snoops, needed for cache coherency.

USB is a particular problem, because unlike other devices (like IDE)
which only do busmaster when active, USB does them to its task list *all
the time*. This is inherent in the hardware's design.

Software can mitigate this in several ways. First, if there are no
devices attached, then we can put the host controller into Global
Suspend until a device is inserted. UHCI does not scan its task list
when suspended. Windows does this (and so does the Linux "uhci" driver,
but not "uhci-usb"). Another way is selective suspend. In this case, if
*all* the attached devices suspend themselves, we can suspend the HC.
Linux doesn't do this, but Win XP does. The worst scenario is any active
device on the USB. This rules out any technique to minimize busmaster
activity.

This is one reason why laptops have not switched to using internal USB
connections for mouse and keyboard.

Regards -- Andy


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