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Date: Fri, 19 May 2017 13:09:51 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Aaron Lu <aaron.lu@intel.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>, Huang Ying <ying.huang@intel.com>
Subject: Re: [PATCH resend] smp: avoid sending needless IPI in
 smp_call_function_many()
Message-ID: <20170519110951.afpvoewwmszdnob5@hirez.programming.kicks-ass.net>
References: <20170428131944.11928-1-aaron.lu@intel.com>
 <20170519075331.GE2084@aaronlu.sh.intel.com>
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On Fri, May 19, 2017 at 03:53:31PM +0800, Aaron Lu wrote:
> @@ -434,6 +442,7 @@ void smp_call_function_many(const struct cpumask *mask,
>  	if (unlikely(!cpumask_weight(cfd->cpumask)))
>  		return;

Another thing that occurred to me while staring at that function, is
that we could move:

	cpumask_and(cfd->cpumask, mask, cpu_online_mask);

to the very begin of that function, that would then obviate the need for
that cpumask_weight() test afaict.


I'm not sure its worth the trouble, but it would make the function
slightly easier to look at.