linux-kernel - Re: [PATCH RFC] kvm: optimize out smp_mb using srcu_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 31 Oct 2013 13:32:59 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	paulmck@...ux.vnet.ibm.com,
	linux-kernel <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
	gleb@...hat.com
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@...hat.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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/