linux-kernel - Re: [PATCH v2 2/5] sched: Teach scheduler to understand ONRQ

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Message-ID: <20140729161928.GA31298@redhat.com>
Date:	Tue, 29 Jul 2014 18:19:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <ktkhai@...allels.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Kirill Tkhai <tkhai@...dex.ru>, linux-kernel@...r.kernel.org,
	nicolas.pitre@...aro.org, pjt@...gle.com, rostedt@...dmis.org,
	umgwanakikbuti@...il.com, tim.c.chen@...ux.intel.com,
	mingo@...nel.org
Subject: Re: [PATCH v2 2/5] sched: Teach scheduler to understand
	ONRQ_MIGRATING state

On 07/29, Kirill Tkhai wrote:
>
> How about this? Everything is inside task_rq_lock() now. The patch
> became much less.

And with this change task_migrating() is not possible under
task_rq_lock() or __task_rq_lock(). This means that 1/5 can be simplified
too.

__migrate_swap_task() is probably the notable exception...

Off-topic, but it takes 2 ->pi_lock's. This means it can deadlock with
try_to_wake_up_local() (if a 3rd process does ttwu() and waits for
->on_cpu == 0). But I guess __migrate_swap_task() should not play with
PF_WQ_WORKER threads.

Oleg.

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