Re: [RFC PATCH 3/3] x86,smp: auto tune spinlock backoff delay factor

From: Rik van Riel
Date: Fri Dec 21 2012 - 22:55:12 EST

On 12/21/2012 10:49 PM, Steven Rostedt wrote:
On Fri, Dec 21, 2012 at 09:51:35PM -0500, Rik van Riel wrote:

However, since spinlock contention should not be the
usual state, and all a scalable lock does is make sure
that N+1 CPUs does not perform worse than N CPUs, using
scalable locks is a stop-gap measure.

I believe a stop-gap measure should be kept as simple as
we can. I am willing to consider moving to a per-lock
delay factor if we can figure out an easy way to do it,
but I would like to avoid too much extra complexity...


I like your solution. It's rather simple and simple solutions tend to
end up being the closest to optimal. The more complex a solution gets,
the more it starts chasing fireflies.

Anyway, I'd like to see this code tested, and more benchmarks run
against it.

Absolutely. I would love to see if this code actually
causes regressions anywhere.

It is simple enough that I suspect it will not, but there
really is only one way to find out.

The more people test this with different workloads on
different SMP systems, the better.

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