linux-kernel - Re: [PATCH 04/21] sched: implement scheduler notifiers

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Message-ID: <1258403365.3961.15.camel@laptop>
Date:	Mon, 16 Nov 2009 21:29:25 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, jeff@...zik.org, mingo@...e.hu,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com,
	torvalds@...ux-foundation.org, avi@...hat.com, andi@...stfloor.org,
	fweisbec@...il.com
Subject: Re: [PATCH 04/21] sched: implement scheduler notifiers

On Tue, 2009-11-17 at 03:54 +0900, Tejun Heo wrote:
> Peter Zijlstra wrote:
> > I really hate exposing activate/deactivate.
> > 
> > You say:
> > 
> >> Activated and deactivated are called
> >> when a task's readiness to run changes.
> > 
> > How is that not clear from the out hook? It would seem to me that when
> > you get scheduled out with a p->state != TASK_RUNNING you're not ready.
> 
> In that in OUT hook the next task to switch to is already determined
> and it wouldn't be symmetric with activate (but I suppose we can match
> the symmetry from activate side).  If deactivate/activate/in/out
> events are too low level,

Not too low, just wrong. Most functions operating on the scheduler state
like sys_renice(), sys_sched_setscheduler() etc.. all do a
deactivate/activate series, even though the task at hand never goes
through a sleep or blocking state.

>  we can have sleep/ready/run hooks instead.

I would much prefer that, sleep/ready are significantly different from
deactivate/activate.

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