linux-kernel - Re: [PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt

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Date:	Fri, 01 Feb 2013 01:57:54 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt_tasks()



31.01.2013, 20:08, "Steven Rostedt" <rostedt@...dmis.org>:
> On Mon, 2013-01-28 at 03:46 +0400, Kirill Tkhai wrote:
>
>>  The patch aims to decrease the number of calls of push_rt_task()
>>  in push_rt_tasks().
>>
>>  It's not necessary to push more than 'num_online_cpus() - 1' tasks.
>>  If just pushed task doesn't leave its new CPU during our local call
>>  of push_rt_tasks() than we won't push another task to the CPU.
>>  If it leave or change priority than it will pull new task by itself.
>
> I'm curious. Have you hit situations where this was an issue? Or was
> this just discovered by code review?

No, I did't hit this situation. It's impossible to hook every situation.

Thanks for your explanation.

Kirill

>
> -- Steve
>
>>  Signed-off-by: Kirill V Tkhai <tkhai@...dex.ru>
>>  CC: Steven Rostedt <rostedt@...dmis.org>
>>  CC: Ingo Molnar <mingo@...nel.org>
>>  CC: Peter Zijlstra <peterz@...radead.org>
>>  CC: linux-rt-users <linux-rt-users@...r.kernel.org>
>>  ---
>>   kernel/sched/rt.c |    4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>  diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>>  index 4e8f0f4..edf046d 100644
>>  --- a/kernel/sched/rt.c
>>  +++ b/kernel/sched/rt.c
>>  @@ -1703,8 +1703,10 @@ out:
>>
>>   static void push_rt_tasks(struct rq *rq)
>>   {
>>  + int num_cpus = num_online_cpus() - 1;
>>  +
>>           /* push_rt_task will return true if it moved an RT */
>>  - while (push_rt_task(rq))
>>  + while (push_rt_task(rq) && --num_cpus > 0)
>>                   ;
>>   }
--
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