linux-kernel - Re: [RFC] Extend mwait idle to optimize away IPIs when possible

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Message-ID: <1328901567.25989.51.camel@laptop>
Date:	Fri, 10 Feb 2012 20:19:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] Extend mwait idle to optimize away IPIs when possible

On Mon, 2012-02-06 at 12:42 -0800, Venkatesh Pallipadi wrote:
> smp_call_function_single and ttwu_queue_remote sends unconditional IPI
> to target CPU. However, if the target CPU is in mwait based idle, we can
> do IPI-less wakeups using the magical powers of monitor-mwait. 

So I was thinking, why not change native_smp_send_reschedule() and
native_send_call_func_single_ipi() and keep the change entirely inside
the arch?

Ideally its only APIC/idle that know about this detail, the scheduler
(or other consumers) really don't care about how the other cpu comes to
run the callback.

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