Subject: Re: [RFC] Extend mwait idle to optimize away IPIs when possible
From: Peter Zijlstra <peterz@infradead.org>
To: Venkatesh Pallipadi <venki@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Aaron Durbin <adurbin@google.com>, Paul Turner <pjt@google.com>,
        linux-kernel@vger.kernel.org
In-Reply-To: <1328560933-3037-1-git-send-email-venki@google.com>
References: <1328560933-3037-1-git-send-email-venki@google.com>
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Date: Fri, 10 Feb 2012 20:19:27 +0100
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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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