linux-kernel - Re: [PATCH 1/2] sched: normalize sleeper's vruntime during group change

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Message-ID: <1285934368.2144.60.camel@laptop>
Date:	Fri, 01 Oct 2010 13:59:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dima Zavin <dima@...roid.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Mike Galbraith <efault@....de>,
	Arve Hjønnevåg <arve@...roid.com>
Subject: Re: [PATCH 1/2] sched: normalize sleeper's vruntime during group
 change

On Thu, 2010-09-30 at 12:14 -0700, Dima Zavin wrote:
> 
> > Please explain this stuff..
> 
> The situation today is quite bad for sleeping tasks. Currently, when
> you move a sleeping thread between cgroups, the thread can retain its
> old vruntime value if the old group was far ahead of the new group
> since it essentially does a max(se->vruntime, new_vruntime) in
> place_entity. This can prevent the task from running for a very long
> time. That is what this patch was trying to address. It normalizes the
> sleeper thread's vruntime before moving it to the new group.
> 
> 

Hrm,.. ok, I tend to not use this cgroup gunk more that I absolutely
have to, so I'll take your word for it.

But doesn't normal cross-cpu task migration already solve this problem?
Therefore wouldn't it be possible to adapt/extend that code to also deal
with this particular issue?

It would avoid growing more cgroup fudge..
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