linux-kernel - Re: [patch 1/2] add ALL_CPUS option to stop_machine

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Message-ID: <20080229023909.GA3440@redhat.com>
Date:	Thu, 28 Feb 2008 21:39:09 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Max Krasnyanskiy <maxk@...lcomm.com>, akpm@...ux-foundation.org,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 1/2] add ALL_CPUS option to stop_machine_run()

On Thu, Feb 28, 2008 at 05:14:30PM -0500, Mathieu Desnoyers wrote:
> * Max Krasnyanskiy (maxk@...lcomm.com) wrote:
> > Jason Baron wrote:
> >> -allow stop_mahcine_run() to call a function on all cpus. Calling  
> >> stop_machine_run() with a 'ALL_CPUS' invokes this new behavior.
> >>  stop_machine_run() proceeds as normal until the calling cpu has
> >>  invoked 'fn'. Then, we tell all the other cpus to call 'fn'.
> >
> > Jason, we're actually trying to reduce the usage of the stop_machine in 
> > general. It's a very big hammer that kills latencies and stuff. It'd be 
> > nice if we did not introduce any more dependencies on it. I guess in some 
> > case there is simply no other way to handle what need to do. But please 
> > think twice
> > (or more :)).
> >
> > Max
> >
> >
> 
> I have a "more complex" immediate value implementation that does not
> depend on such heavy lock. I made this simplified version because Rusty
> preferred it, although I say from the beginning that it kills interrupt
> latency. I could propose the atomic, nmi-safe version directly if enough
> people are in favor of it.
> 
> Mathieu
> 

to me the updating of the immdiate values isn't the critical path, but 
obviously i'd be in favor of a more efficient implementation.

-Jason
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