linux-kernel - Re: [PATCH v2 2/2] x86/pat: Avoid contention on cpa

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Message-ID: <20120822100755.GA26323@gmail.com>
Date:	Wed, 22 Aug 2012 12:07:55 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Ido Yariv <ido@...ery.com>, "H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH v2 2/2] x86/pat: Avoid contention on cpa_lock if possible


* Ido Yariv <ido@...ery.com> wrote:

> Hi Ingo,
> 
> On Wed, Aug 22, 2012 at 10:47:02AM +0200, Ingo Molnar wrote:
> > 
> > * Ido Yariv <ido@...ery.com> wrote:
> > 
> > > vSMP Foundation does not require to serialize CPA by guaranteeing that
> > > the most recent TLB entry will always be used.
> > > 
> > > To avoid needless contention on cpa_lock, do not lock/unlock it if it
> > > isn't necessary.
> > > 
> > > Based on work by Shai Fultheim <shai@...lemp.com>.
> > > 
> > > Signed-off-by: Ido Yariv <ido@...ery.com>
> > > Acked-by: Shai Fultheim <shai@...lemp.com>
> > > ---
> > > Changes from v1:
> > > - Use a synthetic CPUID bit and a use static_cpu_has() as suggested by
> > >   H. Peter Avnin
> > > 
> > >  arch/x86/include/asm/cpufeature.h |    1 +
> > >  arch/x86/kernel/vsmp_64.c         |   10 ++++++++++
> > >  arch/x86/mm/pageattr.c            |   30 +++++++++++++++++++++---------
> > >  3 files changed, 32 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> > > index 6b7ee5f..92303a0 100644
> > > --- a/arch/x86/include/asm/cpufeature.h
> > > +++ b/arch/x86/include/asm/cpufeature.h
> > > @@ -97,6 +97,7 @@
> > >  #define X86_FEATURE_EXTD_APICID	(3*32+26) /* has extended APICID (8 bits) */
> > >  #define X86_FEATURE_AMD_DCM     (3*32+27) /* multi-node processor */
> > >  #define X86_FEATURE_APERFMPERF	(3*32+28) /* APERFMPERF */
> > > +#define X86_FEATURE_NO_CPA_LOCK	(3*32+29) /* Serializing cpa is not required */
> > 
> > Patch looks mostly good, but could we please use some more 
> > hardware-ish name, instead of referring to a kernel lock?
> 
> Sure thing. How about X86_FEATURE_TLB_RELIABLE?

Yeah, something like that. Maybe hpa can think of something 
better?

Thanks,

	Ingo
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