linux-kernel - Re: [PATCH v2 2/2] ksm: Provide support to use deferrable timers for scanner thread

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Date:	Thu, 31 Jul 2014 11:07:44 +0530
From:	Chintan Pandya <cpandya@...eaurora.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	tglx@...utronix.de, john.stultz@...aro.org, peterz@...radead.org,
	mingo@...hat.com, hughd@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] ksm: Provide support to use deferrable timers
 for scanner thread

On 07/31/2014 03:17 AM, Andrew Morton wrote:
> On Fri, 25 Jul 2014 20:18:18 +0530 Chintan Pandya<cpandya@...eaurora.org>  wrote:
>
>> KSM thread to scan pages is scheduled on definite timeout. That wakes
>> up CPU from idle state and hence may affect the power consumption.
>> Provide an optional support to use deferrable timer which suites
>> low-power use-cases.
>>
>> Typically, on our setup we observed, 10% less power consumption with
>> some use-cases in which CPU goes to power collapse frequently. For
>> example, playing audio while typically CPU remains idle.
>>
>> To enable deferrable timers,
>> $ echo 1>  /sys/kernel/mm/ksm/deferrable_timer
>
> This could not have been the version which you tested.  What's up?

My bad :( I will be careful next time
>
> --- a/mm/ksm.c~ksm-provide-support-to-use-deferrable-timers-for-scanner-thread-fix-fix-2
> +++ a/mm/ksm.c
> @@ -1720,8 +1720,6 @@ static int ksmd_should_run(void)
>
>   static int ksm_scan_thread(void *nothing)
>   {
> -	signed long to;
> -
>   	set_freezable();
>   	set_user_nice(current, 5);
>
> @@ -1735,7 +1733,9 @@ static int ksm_scan_thread(void *nothing
>   		try_to_freeze();
>
>   		if (ksmd_should_run()) {
> -			timeout = msecs_to_jiffies(ksm_thread_sleep_millisecs);
> +			signed long to;
> +
> +			to = msecs_to_jiffies(ksm_thread_sleep_millisecs);
>   			if (use_deferrable_timer)
>   				schedule_timeout_deferrable_interruptible(to);
>   			else
> _
>


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