linux-kernel - Re: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree

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Date:	Wed, 02 Jan 2008 18:41:55 -0500
From:	Mark Lord <lkml@....ca>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>, abelay@...ell.com,
	lenb@...nel.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree

Arjan van de Ven wrote:
> On Fri, 30 Nov 2007 22:31:17 -0500
> Mark Lord <lkml@....ca> wrote:
> 
>> Arjan van de Ven wrote:
>>> On Fri, 30 Nov 2007 22:14:08 -0500
>>> Mark Lord <lkml@....ca> wrote:
>>>
>>>>> in -mm there is.. the QoS stuff allows you to set maximum
>>>>> tolerable
>>>> ..
>>>>
>>>> That's encouraging, I think, but not for 2.6.24.
>>>>
>>>>> latency. If your app cant take any latency, you should set
>>>>> those... and the side effect is that the kernel will not do
>>>>> long-latency C-states or P-state transitions..
>>>> ..
>>>>
>>>> I don't mind the cpufreq changing (actually, I want it to drop in
>>>> cpugfreq to save power and keep the fan off), but the C-states just
>>>> kill this app.
>>>>
>>>> The app is VMware.  I force the max_state=1 when launching,
>>> ah but then its' even easier... and can be done in 2.6.24 already.
>>> VMWare after all has a kernel module, and the latency stuff is in
>>> 2.6.23 and 2.6.24 available inside the kernel already.
>> ..
>>
>> Oh, I'm perfectly happy to write my own kernel module if that's what
> 
> all you need to do in your kernel module is call
> 
> add_latency_constraint("mark_wants_his_mouse", 5);
> 
> or so
..

Dredging up an old regression again now:

The "make my own module to replace /sys/.../max_cstate" doesn't work
for the single-core machine we use a lot around here.

VMware is totally sluggish unless I go to another text window and do this:

    while ( true ); do echo -n ; done

At which point VMware performs well again,
the same as with "echo 1 > max_cstate" in 2.6.23.

Anyone got any suggestions on how to fix this regression
or work around it for 2.6.24 ?

Thanks 


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