RE: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree

[Pallipadi, Venkatesh]

>-----Original Message-----
>From: Mark Lord [mailto:lkml@xxxxxx] 
>Sent: Wednesday, January 02, 2008 3:42 PM
>To: Arjan van de Ven
>Cc: Pallipadi, Venkatesh; Andrew Morton; abelay@xxxxxxxxxx; 
>lenb@xxxxxxxxxx; Ingo Molnar; linux-kernel@xxxxxxxxxxxxxxx; 
>linux-acpi@xxxxxxxxxxxxxxx
>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@xxxxxx> wrote:
>> 
>>> Arjan van de Ven wrote:
>>>> On Fri, 30 Nov 2007 22:14:08 -0500
>>>> Mark Lord <lkml@xxxxxx> 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 ?
>

Easiest and clean way to do it is to have a driver with
set_acceptable_latency() for 1uS or so in init and
remove_acceptable_latency() at exit.

Thanks,
Venki
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