Re: [RFC PATCH 0/3] Fix ebizzy performance regression on IvyBridge due to X86 TLB range flush

[Ingo Molnar <mingo@kernel.org>]

* Mel Gorman <mgorman@suse.de> wrote:

> > [...]
> >
> > stddev appears to be rather large especially around a client count 
> > of 7-8. It will be difficult to fine-tune the TLB range flush 
> > constants if noise is too large.
> 
> The number of iterations were very low to have high confidence of 
> the figures. The high standard deviation for 5 clients was a single 
> large outlier. It potentially could be stabilised to some extent by 
> bumping up the number of iterations a lot and using percentiles 
> instead of means.

Fair enough - and you were bisecting so length of runtime and 
confidence of detection were obviously the primary concerns.

> I'm a bit wary of optimising the TLB flush ranges based on the 
> benchmark even if we stabilised the figures. [...]

Absolutely - but they do appear to be pretty 'adversarial' to the TLB 
optimization, with a measurable slowdown in a pretty complex, 
real-life workload pattern.

So future tuning efforts will have to take such workloads into effect 
as well, to make sure we don't regress again.

Thanks,

	Ingo