Messages in this thread | | | Date | Thu, 31 Oct 2013 13:32:59 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH RFC] kvm: optimize out smp_mb using srcu_read_unlock |
| |
On Thu, Oct 31, 2013 at 12:14:15PM +0100, Paolo Bonzini wrote: > 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@redhat.com> > > Across how many runs?
It's the experiment that vmexit test does: it runs for 2^30 cycles, then divides the number of cycles by the number of iterations. You get in the ballpark of 1300000 iterations normally.
> 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. > > Paolo
"All runs in that ballpark".
-- MST
| |