linux-kernel - Re: [PATCH] sched: Remove broken check for skip clock update

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Message-ID: <CAFTL4hymZ9GqC+XEec0WGJij99jc_K3pdQZ48t0eKU45PzQEJg@mail.gmail.com>
Date:	Tue, 8 Jan 2013 02:55:12 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] sched: Remove broken check for skip clock update

2013/1/8 Steven Rostedt <rostedt@...dmis.org>:
> On Tue, 2013-01-08 at 02:07 +0100, Frederic Weisbecker wrote:
>> rq->skip_clock_update shouldn't be negative. Thus the check
>> in put_prev_task() is useless.
>>
>> It was probably intended to do the following check:
>>
>>       if (prev->on_rq && !rq->skip_clock_update)
>>
>> We only want to update the clock if the current task is
>> not voluntarily sleeping: otherwise deactivate_task()
>> already did the rq clock update in schedule(). But we want
>> to ignore that update if a ttwu did it for us, in which case
>> rq->skip_clock_update is 1.
>>
>> But update_rq_clock() already takes care of that so we
>> can just remove the broken condition.
>
> kernel/sched/rt.c:
>
>                                 /*
>                                  * Force a clock update if the CPU was idle,
>                                  * lest wakeup -> unthrottle time accumulate.
>                                  */
>                                 if (rt_rq->rt_nr_running && rq->curr == rq->idle)
>                                         rq->skip_clock_update = -1;

Grr, I knew I was missing something!

Ok let's drop that patch then.
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