linux-kernel - Re: [PATCH 0/3] hrtimer: HRTIMER_STATE

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Message-ID: <20150608155628.GB23743@redhat.com>
Date:	Mon, 8 Jun 2015 17:56:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	umgwanakikbuti@...il.com, mingo@...e.hu, ktkhai@...allels.com,
	rostedt@...dmis.org, tglx@...utronix.de, juri.lelli@...il.com,
	pang.xunlei@...aro.org, wanpeng.li@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] hrtimer: HRTIMER_STATE_ fixes

On 06/08, Peter Zijlstra wrote:
>
> On Mon, 2015-06-08 at 17:10 +0200, Oleg Nesterov wrote:
> > On 06/08, Peter Zijlstra wrote:
> > >
> > > > I tend to agree, but I think its a pre-existing problem, not one
> > > > introduced by my proposed patch.
> > >
> > > Something like this would fix that I think. It fully preserves
> > > timer->state over hrtimer_start_range_ns().
> >
> > Yes, but I think we can do a bit better.
> >
> > Only for initial review, I need to re-check this...
>
> I'm having a wee bit of bother spotting how you version is 'better'.
>
> > And. I think that after you remove STATE_CALLBACK we can even kill
> > timer->state altogether, but this is another story.
>
> Ah, yes, we could introduce timerqueue_is_queued() which uses
> RB_EMPTY_NODE(). Obviating the need for hrtimer::state entirely.

Yes exactly.

And to me 2/3 looks like a cleanup in any case, __remove_hrtimer()
should do nothing with other bits. Yes,

	timer->state |= HRTIMER_STATE_CALLBACK;
	__remove_hrtimer(timer, base, true, 0);

in __run_hrtimer() looks worse than __remove_hrtimer(CALLBACK), but
you are going to kill STATE_CALLBACK. And this should even simplify
your patch a little bit.

But I agree, this is minor and subjective.

Oleg.

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