linux-kernel - Re: clock drift in set_task

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Message-ID: <20100906065229.GA14609@elte.hu>
Date:	Mon, 6 Sep 2010 08:52:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jack Daniel <wanders.thirst@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, pjohn@...sta.com
Subject: Re: clock drift in set_task_cpu()


* Jack Daniel <wanders.thirst@...il.com> wrote:

> Hi Ingo,
>
> [...]
> 
> Any chance that you will be pulling in this fix ?

It's already upstream, as of v2.6.36-rc3. See the commit notification 
email below from Aug 19.

Thanks,

	Ingo

----- Forwarded message from tip-bot for Peter Zijlstra <peterz@...radead.org> -----

Date: Fri, 20 Aug 2010 14:16:14 GMT
From: tip-bot for Peter Zijlstra <peterz@...radead.org>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, peterz@...radead.org, pjohn@...sta.com,
	wanders.thirst@...il.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/urgent] sched: Fix rq->clock synchronization when migrating tasks

Commit-ID:  861d034ee814917a83bd5de4b26e3b8336ddeeb8
Gitweb:     http://git.kernel.org/tip/861d034ee814917a83bd5de4b26e3b8336ddeeb8
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 19 Aug 2010 13:31:43 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 20 Aug 2010 14:59:01 +0200

sched: Fix rq->clock synchronization when migrating tasks

sched_fork() -- we do task placement in ->task_fork_fair() ensure we
  update_rq_clock() so we work with current time. We leave the vruntime
  in relative state, so the time delay until wake_up_new_task() doesn't
  matter.

wake_up_new_task() -- Since task_fork_fair() left p->vruntime in
  relative state we can safely migrate, the activate_task() on the
  remote rq will call update_rq_clock() and causes the clock to be
  synced (enough).

Tested-by: Jack Daniel <wanders.thirst@...il.com>
Tested-by: Philby John <pjohn@...sta.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1281002322.1923.1708.camel@...top>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 806d1b2..ab661eb 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3752,6 +3752,8 @@ static void task_fork_fair(struct task_struct *p)
 
 	raw_spin_lock_irqsave(&rq->lock, flags);
 
+	update_rq_clock(rq);
+
 	if (unlikely(task_cpu(p) != this_cpu))
 		__set_task_cpu(p, this_cpu);
 

----- End forwarded message -----
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