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

[Rik van Riel <riel@redhat.com>]

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...
>
> Rik,
>
> 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.