linux-kernel - Re: [v2 PATCH 1/4] timers: framework to identify pinned timers.

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Date:	Fri, 6 Mar 2009 16:03:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	a.p.zijlstra@...llo.nl, ego@...ibm.com, tglx@...utronix.de,
	mingo@...e.hu, andi@...stfloor.org, venkatesh.pallipadi@...el.com,
	vatsa@...ux.vnet.ibm.com, arjan@...radead.org,
	svaidy@...ux.vnet.ibm.com
Subject: Re: [v2 PATCH 1/4] timers: framework to identify pinned timers.

On 03/06, Arun R Bharadwaj wrote:
>
> * Oleg Nesterov <oleg@...hat.com> [2009-03-05 17:53:40]:
>
> > > @@ -736,6 +759,7 @@ void add_timer_on(struct timer_list *tim
> > >  	struct tvec_base *base = per_cpu(tvec_bases, cpu);
> > >  	unsigned long flags;
> > >
> > > +	timer_set_pinned(timer);
> >
> > But we never clear TBASE_PINNED_FLAG?
> >
> > If we use mod_timer() next time, the timer remains "pinned". I do not say
> > this is really wrong, but a bit strange imho.
> >
> > Oleg.
> >
>
> The pinned timer would expect to continue firing on the same CPU
> although it does a mod_timer() the next time, right?

Why? Let's suppose we call queue_delayed_work_on(), and next time
we use queue_delayed_work() with the same dwork. The timer is still
pinned, this doesn't look consistent to me.

> Thats why I have not cleared the TBASE_PINNED_FLAG.

Personally, I don't like this flag. I think that "pinned" should
be the argument for mod_timer(), not the "property" of timer_list.

Oleg.

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