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Date: Fri, 11 Oct 2013 08:09:44 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Johannes Weiner <hannes@cmpxchg.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, Oct 10, 2013 at 12:04 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > I'm wondering if we can have a for_each_cpu() that only disables 
> > preemption in the loop.
> 
> I think we'd generally want to have it be something the loop asks for.
> 
> If the loop is just some kind of "gather statistics" thing, I don't 
> think it's required. The cost per loop is so low (usually adding up a 
> couple of words) that the downside drowns the upside.
> 
> And we could easily look at MAXSMP (or NR_CPUS) at compile-time, and not 
> do it for common small values (although it looks like Fedora defaults to 
> 128 CPU's for their distro kernels, which seems a bit excessive - too 
> many by far for normal people, too few for the crazy big ones).

Ubuntu has it at 256, so I guess Fedora is even a bit conservative ;-)

Thanks,

	Ingo