linux-kernel - Re: [v4 RFC PATCH 1/4] timers: Framework for identifying pinned timers

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Message-ID: <20090402050919.GA8813@linux.vnet.ibm.com>
Date:	Thu, 2 Apr 2009 10:39:19 +0530
From:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
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, venkatesh.pallipadi@...el.com,
	vatsa@...ux.vnet.ibm.com, arjan@...radead.org,
	svaidy@...ux.vnet.ibm.com, Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [v4 RFC PATCH 1/4] timers: Framework for identifying pinned
	timers

* Andi Kleen <andi@...stfloor.org> [2009-04-01 13:41:46]:

> On Wed, Apr 01, 2009 at 05:02:58PM +0530, Arun R Bharadwaj wrote:
> > * Arun R Bharadwaj <arun@...ux.vnet.ibm.com> [2009-04-01 17:01:28]:
> > 
> > This patch creates a new framework for identifying cpu-pinned timers
> > and hrtimers.
> > 
> > 
> > This framework is needed because pinned timers are expected to fire on
> > the same CPU on which they are queued. So it is essential to identify
> > these and not migrate them, in case there are any.
> 
> How would that interact with add_timer_on()? You currently only
> support the current CPU, don't you?
> 
> e.g. the new tip x86 machine check polling code relies on add_timer_on
> staying on that CPU.
>

Pinned timers are directly related to add_timer_on().
So I assume that whatever timer is queued using add_timer_on() is
supposed to be a pinned timer.
Currently, we can stay on one CPU and still queue a pinned timer on
some other CPU. We can mark those timers as 'pinned' to that
particular CPU.

--arun

> -Andi
> 
> -- 
> ak@...ux.intel.com -- Speaking for myself only.
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