Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Thu, Oct 10, 2013 at 12:04 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> 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
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