linux-kernel - RE: [PATCH] sched: recover sched_yield task running time increase

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Message-ID: <6E3BC7F7C9A4BF4286DD4C043110F30B4BBA01D83D@shsmsx502.ccr.corp.intel.com>
Date:	Wed, 6 Apr 2011 21:28:38 +0800
From:	"Shi, Alex" <alex.shi@...el.com>
To:	Mike Galbraith <efault@....de>
CC:	Rik van Riel <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: RE: [PATCH] sched: recover sched_yield task running time increase

>> > NACK
>> >
>> > This was switched off by default and under
>> > the sysctl sched_compat_yield for a reason.
>> >
>> > Reintroducing it under that sysctl option
>> > may be acceptable, but by default it would
>> > be doing the wrong thing for other workloads.
>>
>> I can implement this as sysctl option. But when I checked again the man
>> page of sched_yield. I have some concerns on this.
>>
>> ----
>>        int sched_yield(void);
>>
>> DESCRIPTION
>>        A  process  can  relinquish  the processor voluntarily without blocking by calling sched_yield().
>>        The process will then be moved to the end of the queue for its static priority and a new  process
>>        gets to run.
>> ----
>>
>> If a application calls sched_yield system call, most of time it is not
>> want to be launched again right now. so the man page said "the caller
>> process will then be moved to the _end_ of the queue..."
>
>Moving a yielding nice 0 task behind a SCHED_IDLE (or nice 19) task
>could be incredibly painful.

Good reminder! Do you have more detailed idea on this? 
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