RE: [patch] i386 dynamic ticks 2.6.13-rc4 (code reordered)

Pallipadi, Venkatesh
2005-08-08T18:38:03Z

>-----Original Message-----
>From: linux-kernel-owner@vger.kernel.org
>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of
>Stefan Seyfried
>Sent: Sunday, August 07, 2005 10:43 PM
>To: Con Kolivas
>Cc: tony@atomide.com; ck@vds.kolivas.org;
>tuukka.tikkanen@elektrobit.com; linux-kernel@vger.kernel.org;
>tytso@mit.edu
>Subject: Re: [patch] i386 dynamic ticks 2.6.13-rc4 (code reordered)
>
>Con Kolivas wrote:
>
>>> When I enabled dynamic tick using:
>>>
>>> echo 1 > /sys/devices/system/timer/timer0/dyn_tick_state
>>>
>>> The number of ticks dropped down to 60-70 HZ, bus mastering activity
>>> jumpped up to being almost always active,
>>
>> Anyone know why this would happen?
>
>This is just a guess, without any actual code-reading:
>Maybe the C-state decision process just relies on being called every
>tick, so "after X ticks with no BM activity, go to next deeper
>C state".
>As long as 1000 ticks per second are coming in, everything is fine and
>we enter C[n+1] after X miliseconds without BM activity. Now if there
>are only 60-70 ticks per second, you never get X ticks without BM
>activity so you never go deeper than C2.
>
>Just a guess.

That is correct. The C-state policy right now looks at jiffies to decide
on which C-state to go to (instead of absolute time).
This patch from Thomas should help with respect to going to proper
C-state in presence of dynamic tick.
http://lkml.org/lkml/2005/4/19/96

Thanks,
Venki