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

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Message-ID: <20090306061438.GB9190@linux.vnet.ibm.com>
Date:	Fri, 6 Mar 2009 11:44:38 +0530
From:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.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.

* Oleg Nesterov <oleg@...hat.com> [2009-03-05 17:53:40]:

> On 03/04, Arun R Bharadwaj wrote:
> >
> > +static inline unsigned long tbase_get_flag_bits(struct timer_list *timer)
> > +{
> > +	return tbase_get_deferrable(timer->base) |
> > +				tbase_get_pinned(timer->base);
> > +}
> 
> I'd say this looks a bit strange. Hopefully compiler can optimize this code
> to return (unsigned long)base & (TBASE_DEFERRABLE_FLAG | TBASE_PINNED_FLAG).
>

Yes, it does.

> > @@ -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?
Thats why I have not cleared the TBASE_PINNED_FLAG.

--arun
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