linux-kernel - Re: [patch for 2.6.30 2/2] arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU interrupts

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Message-ID: <20090412000605.GA23869@redhat.com>
Date:	Sat, 11 Apr 2009 20:06:05 -0400
From:	Dave Jones <davej@...hat.com>
To:	akpm@...ux-foundation.org
Cc:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, efault@....de, len.brown@...el.com,
	mingo@...e.hu, rusty@...tcorp.com.au, tglx@...utronix.de,
	venkatesh.pallipadi@...el.com, yakui.zhao@...el.com,
	yanmin_zhang@...ux.intel.com
Subject: Re: [patch for 2.6.30 2/2]
	arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c: avoid cross-CPU
	interrupts

On Fri, Apr 10, 2009 at 11:17:18PM -0700, Andrew Morton wrote:
 > From: Andrew Morton <akpm@...ux-foundation.org>
 > 
 > In drv_read(), check to see whether we can run the rdmsr() on the current
 > CPU.  If so, do that.  So smp_call_function_single() can avoid the IPI.

Wouldn't it be a better to make smp_call_function_single do this check
itself, so all callers benefit from this optimisation?

*looks*

Wait, won't this already be caught by this code in smp_call_function_single() ?

286         this_cpu = get_cpu();
...
291         if (cpu == this_cpu) {
292                 local_irq_save(flags);
293                 func(info);
294                 local_irq_restore(flags);
295         } else {



	Dave 

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