linux-kernel - Re: [PATCH RESEND] sched/nohz: Affine unpinned timers to housekeepers

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Date:	Mon, 24 Aug 2015 09:23:17 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Vatika Harlalka <vatikaharlalka@...il.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH RESEND] sched/nohz: Affine unpinned timers to
 housekeepers

On Mon, 2015-08-24 at 08:44 +0200, Ingo Molnar wrote:

> the 'housekeeping CPU' is essentially the boot CPU. Yet we dedicate a full mask to 
> it (housekeeping_mask - a variable mask to begin with) and recover the 
> housekeeping CPU via:
> 
> +       return cpumask_any_and(housekeeping_mask, cpu_online_mask);

There can be, and had better be if box is big, multiple housekeepers.

Imagine a NO_HZ_FULL_ALL kernel on an SGI beast from hell.  Offloading
8191 CPUs onto poor little CPU0 probably wouldn't work out well :)

	-Mike

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