From: Andi Kleen <andi@firstfloor.org>
To: Eial Czerwacki <eial@scalemp.com>
Cc: linux-kernel@vger.kernel.org,
"Shai Fultheim \(Shai\@ScaleMP.com\)" <Shai@scalemp.com>
Subject: Re: [PATCH] APICID: Avoid false sharing on the read mostly x86_cpu_to_apicid
Date: Wed, 26 Oct 2011 01:20:26 -0700 [thread overview]
Message-ID: <m2fwigw4dx.fsf@firstfloor.org> (raw)
In-Reply-To: <4EA6A265.1080506@scalemp.com> (Eial Czerwacki's message of "Tue, 25 Oct 2011 13:49:57 +0200")
Eial Czerwacki <eial@scalemp.com> writes:
> ===================================================================
> --- a/arch/x86/include/asm/smp.h 2010-06-01 09:56:03.000000000 -0700
> +++ b/arch/x86/include/asm/smp.h 2010-06-02 15:59:21.000000000 -0700
> @@ -36,7 +36,8 @@ static inline struct cpumask *cpu_core_m
> return per_cpu(cpu_core_map, cpu);
> }
>
> -DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
> +extern u16 x86_cpu_to_apicid[NR_CPUS];
That's a big waste of memory. On a CONFIG_MAX_SMP kernel compiled for
4096 CPUs you're wasting 8k now on smaller systems. The per cpu
data only allocates what is needed.
NR_CPUS is usually a bad idea and it
Perhaps need a __read_mostly cache line padded per CPU section instead
for cases like this.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
prev parent reply other threads:[~2011-10-26 8:20 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4EA66960.7050907@scalemp.com>
[not found] ` <9B14D1490DDECA4E974F6B9FC9EBAB3140CD274367@VMBX108.ihostexchange.net>
2011-10-25 11:49 ` [PATCH] APICID: Avoid false sharing on the read mostly x86_cpu_to_apicid Eial Czerwacki
2011-10-26 6:21 ` David Rientjes
2011-10-26 6:41 ` Eial Czerwacki
2011-10-26 6:47 ` David Rientjes
2011-10-26 7:01 ` Eial Czerwacki
2011-10-26 8:20 ` Andi Kleen [this message]
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