linux-kernel - Re: sched_setscheduler() vs idle

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Message-ID: <20150601081429.GP19282@twins.programming.kicks-ass.net>
Date:	Mon, 1 Jun 2015 10:14:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	ktkhai@...allels.com
Subject: Re: sched_setscheduler() vs idle_balance() race

On Fri, May 29, 2015 at 08:48:56PM +0200, Mike Galbraith wrote:
> 
> P.S. intel_idle is not all that wonderful on this box.
> 
> -   78.31%  [kernel]       [k] _raw_spin_lock                                                                                                                                                                                              ▒
>    - _raw_spin_lock                                                                                                                                                                                                                        ▒
>       - 94.91% tick_broadcast_oneshot_control                                                                                                                                                                                              ▒

Your DL980 G7 has E7-4800 parts in, right? Which if Wikipedia is
correct, resolves to a Nehalem-EX.

Now the NHM-EX has a fun 'feature' that for (some?) idle states the
local timer stops, so we have to revert back to a global broadcast
timer.

Now go count the number of cpus on your box and then imagine a global
spinlock, oh wait, you already found it ^ :-)
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