linux-kernel - Re: [PATCH 1/3] perf: add context field to perf

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Message-ID: <20110712094205.GB26125@e102144-lin.cambridge.arm.com>
Date:	Tue, 12 Jul 2011 10:42:06 +0100
From:	Will Deacon <will.deacon@....com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	"acme@...stprotocols.net" <acme@...stprotocols.net>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [PATCH 1/3] perf: add context field to perf_event

On Tue, Jul 12, 2011 at 10:36:05AM +0100, Avi Kivity wrote:
> On 07/12/2011 12:31 PM, Peter Zijlstra wrote:
> > >
> > >  But it means that 'current' is not set to the right value.  If the
> > >  function depends on it, then it will misbehave.  And in fact
> > >  preempt_notifier_register(), which is the function we want to call here,
> > >  does depend on current.
> > >
> > >  Of course we need to find more users for this, but I have a feeling this
> > >  will be generally useful.  The alternative is to keep adding bits to
> > >  thread_info::flags.
> >
> > Using TIF_bits sounds like a much better solution for this, wakeups are
> > really rather expensive and its best to avoid extra if at all possible.
> >
> 
> We do need a way to make the task look at them.

... especially without pushing this down into the arch code where I don't
think it belongs.
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