linux-kernel - Re: [PATCH] posixtimers: Fix posix clock monotonicity

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Date:	Tue, 17 Mar 2009 15:31:04 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] posixtimers: Fix posix clock monotonicity

KAMEZAWA Hiroyuki wrote:
> Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> wrote:
> 
>> This patch rehires task_sched_runtime() and thread_group_sched_runtime()
>> which were removed at the time of 2.6.28-rc1.
>>
>> These functions protect the sampling of clock with rq lock.
>> This rq lock is required not to update rq->clock during the sampling.
>> i.e. You may get ((banked runtime before update)+(delta after update)).
>>
> Does clock_gettime() go backward without lock ?

Yes, that's right.

You can find the ancestor of this patch here:
 [RESEND][PATCH] posixtimers: clock_gettime(CLOCK_*_CPUTIME_ID) goes backward
  http://lkml.org/lkml/2009/1/27/18

After the last post, I dug the git-log and found that there were functions,
task_sched_runtime() and thread_group_sched_runtime(), worked fine at the
time of 2.6.27.  I think it is better to reintroduce these functions again
than making almost same function with different name.

Thanks,
H.Seto

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