Re: [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock

From: Paolo Bonzini
Date: Thu Oct 31 2013 - 07:14:26 EST

Il 30/10/2013 20:09, Michael S. Tsirkin ha scritto:
> I noticed that srcu_read_lock/unlock both have a memory barrier,
> so just by moving srcu_read_unlock earlier we can get rid of
> one call to smp_mb().
> Unsurprisingly, the gain is small but measureable using the unit test
> microbenchmark:
> before
> vmcall 1407
> after
> vmcall 1357
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

Across how many runs? Best or average or "all runs were in that
ballpark", :) and what's the minimum/maximum before and after the patch?

As you say the benefit is not surprising, but the experiments should be
documented properly.

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