linux-kernel - Re: [PATCH 2/2] x86: Move x86_cpu_to_apicid to the __read

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Date:	Mon, 7 May 2012 16:07:44 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Vlad Zolotarov <vlad@...lemp.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	alan@...rguk.ukuu.org.uk,
	"Shai Fultheim (Shai@...leMP.com)" <Shai@...lemp.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 2/2] x86: Move x86_cpu_to_apicid to the __read_mostly
 section


* Vlad Zolotarov <vlad@...lemp.com> wrote:

> On Monday, May 07, 2012 01:52:47 pm Ingo Molnar wrote:
> > * Vlad Zolotarov <vlad@...lemp.com> wrote:
> > > From: Shai Fultheim <shai@...lemp.com>
> > > 
> > > x86_cpu_to_apicid is only written to during initialization. Benchmarks
> > > show that moving it to the __read_mostly section helps avoid false
> > > sharing on large multiprocessing systems.
> > > 
> > > Signed-off-by: Shai Fultheim <shai@...lemp.com>
> > > Signed-off-by: Vlad Zolotarov <vlad@...lemp.com>
> > > ---
> > > 
> > >  arch/x86/include/asm/smp.h |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> > > index 0434c40..b9d6c1e 100644
> > > --- a/arch/x86/include/asm/smp.h
> > > +++ b/arch/x86/include/asm/smp.h
> > > @@ -53,7 +53,7 @@ static inline struct cpumask *cpu_llc_shared_mask(int
> > > cpu)
> > > 
> > >  	return per_cpu(cpu_llc_shared_map, cpu);
> > >  
> > >  }
> > > 
> > > -DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
> > > +DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid);
> > > 
> > >  DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
> > >  #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32)
> > >  DECLARE_EARLY_PER_CPU(int, x86_cpu_to_logical_apicid);
> > 
> > Looks like all of the surrounding fields are read mostly as
> > well, only initialized very rarely, during cpu init?
> 
> U r right. At least x86_bios_cpu_apicid is read mostly as 
> well. I'll fix and respin.

Thanks.

> Did u have a chance to look at the other "__read_mostly" patch for fs/buffer.c 
> I've sent?

Haven't been involved with fs/buffer.c for some time, please 
send it to the relevant maintainer:

 $ scripts/get_maintainer.pl -f fs/buffer.c 
 Alexander Viro <viro@...iv.linux.org.uk> (maintainer:FILESYSTEMS (VFS...)
 linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS...)
 linux-kernel@...r.kernel.org (open list)

Thanks,

	Ingo
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