linux-kernel - Re: [PATCH] Trace idle entry and exit times

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Message-ID: <1386392252.5673.31.camel@marge.simpson.net>
Date:	Sat, 07 Dec 2013 05:57:32 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>, lenb@...nel.org,
	tglx@...utronix.de, peterz@...radead.org
Subject: Re: [PATCH] Trace idle entry and exit times

On Fri, 2013-12-06 at 16:46 -0800, Andi Kleen wrote: 
> From: Andi Kleen <ak@...ux.intel.com>
> 
> This patch creates 4 new trace points: one at the beginning of idle,
> one before entering mwait, one after exiting mwait, and one after
> finishing the idle code. This is useful to trace down any
> additional latencies caused by the ever-growing idle code.
> 
> Idle latencies are a common source of performance problems, so it's
> important to be able to measure them.

You mean stuff like.. oh, say 60 cores doing zero work every 12ms
munching ~20% cpu?

-  97.57%  [kernel]          [k] _raw_spin_lock_irqsave                                                                                                                                                                                    ▒
   - _raw_spin_lock_irqsave                                                                                                                                                                                                                ▒
      - 97.02% clockevents_notify                                                                                                                                                                                                          ◆
           intel_idle                                                                                                                                                                                                                      ▒
           cpuidle_idle_call                                                                                                                                                                                                               ▒
           cpu_idle                                                                                                                                                                                                                        ▒
      - 2.97% tick_broadcast_oneshot_control                                                                                                                                                                                               ▒
           tick_notify                                                                                                                                                                                                                     ▒
           notifier_call_chain                                                                                                                                                                                                             ▒
           clockevents_notify                                                                                                                                                                                                              ▒
           intel_idle                                                                                                                                                                                                                      ▒
           cpuidle_idle_call                                                                                                                                                                                                               ▒
           cpu_idle

C2 is super green, it's hug'n the sh*t outta them trees :)

	-Mike

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