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

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Message-Id: <200803031032.03160.rusty@rustcorp.com.au>
Date:	Mon, 3 Mar 2008 10:32:02 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Max Krasnyanskiy <maxk@...lcomm.com>
Cc:	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Kathy Staples <kathy.staples@....ibm.com>
Subject: Re: [patch 1/2] add ALL_CPUS option to stop_machine_run()

On Friday 29 February 2008 09:09:37 Max Krasnyanskiy 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 :)).

Well, by definition modifying an immediate value should be very rare, so it's 
a reasonable candidate.

But stop_machine needs work.  It should not be as heavy as it is.

Cheers,
Rusty.
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