linux-kernel - Re: [PATCH RFC 0/5] apic: eoi optimization support

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Message-ID: <20120507114001.GA15186@gmail.com>
Date:	Mon, 7 May 2012 13:40:01 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	x86@...nel.org, kvm@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, gleb@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/5] apic: eoi optimization support


* Michael S. Tsirkin <mst@...hat.com> wrote:

> On Mon, May 07, 2012 at 12:35:12PM +0200, Ingo Molnar wrote:
> > > Michael S. Tsirkin (5):
> > >   apic: fix typo EIO_ACK -> EOI_ACK and document
> > >   apic: use symbolic APIC_EOI_ACK
> > >   x86: add apic->eoi_write callback
> > >   x86: eoi micro-optimization
> > >   kvm_para: guest side for eoi avoidance
> > > 
> > >  arch/x86/include/asm/apic.h            |   22 ++++++++++++--
> > >  arch/x86/include/asm/apicdef.h         |    2 +-
> > >  arch/x86/include/asm/bitops.h          |    6 ++-
> > >  arch/x86/include/asm/kvm_para.h        |    2 +
> > >  arch/x86/kernel/apic/apic_flat_64.c    |    2 +
> > >  arch/x86/kernel/apic/apic_noop.c       |    1 +
> > >  arch/x86/kernel/apic/apic_numachip.c   |    1 +
> > >  arch/x86/kernel/apic/bigsmp_32.c       |    1 +
> > >  arch/x86/kernel/apic/es7000_32.c       |    2 +
> > >  arch/x86/kernel/apic/numaq_32.c        |    1 +
> > >  arch/x86/kernel/apic/probe_32.c        |    1 +
> > >  arch/x86/kernel/apic/summit_32.c       |    1 +
> > >  arch/x86/kernel/apic/x2apic_cluster.c  |    1 +
> > >  arch/x86/kernel/apic/x2apic_phys.c     |    1 +
> > >  arch/x86/kernel/apic/x2apic_uv_x.c     |    1 +
> > >  arch/x86/kernel/kvm.c                  |   51 ++++++++++++++++++++++++++++++--
> > >  arch/x86/platform/visws/visws_quirks.c |    2 +-
> > >  17 files changed, 88 insertions(+), 10 deletions(-)
> > 
> > No objections from the x86 side.
> 
> Is kvm.git a good tree to merge this through?

Fine to me, but I haven't checked how widely it conflicts with 
existing bits: by the looks of it most of the linecount is on 
the core x86 side, while the kvm change is well concentrated.

> > In terms of advantages, could you please create perf stat 
> > runs that counts the number of MMIOs or so? That should show 
> > a pretty obvious improvement - and that is enough as proof, 
> > no need to try to reproduce the performance win in a noisy 
> > benchmark.
> 
> You mean with kvm PV, right? On real hardware the 
> micro-optimization removes branches and maybe cache-misses but 
> I don't see why would it reduce MMIOs.

Yeah, on KVM. On real hw I doubt it's measurable.

Thanks,

	Ingo
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