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

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Message-ID: <20150824080011.GA23649@gmail.com>
Date:	Mon, 24 Aug 2015 10:00:11 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
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


* Mike Galbraith <umgwanakikbuti@...il.com> wrote:

> On Mon, 2015-08-24 at 09:41 +0200, Ingo Molnar wrote:
> > * Mike Galbraith <umgwanakikbuti@...il.com> wrote:
> > 
> > > 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.
> > 
> > Yes - but that does not seem to be possible via the code right now AFAICS, so 
> > at minimum it's incomplete.
> 
> In master housekeepers are set up in tick_nohz_init().  Everybody who's not a 
> nohz_full CPU is a housekeeper.

Ah, indeed, I missed the nohz_full= boot option:

static int __init tick_nohz_full_setup(char *str)
{
        alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
        if (cpulist_parse(str, tick_nohz_full_mask) < 0) {


Ok, first question is resolved - but the second one, behavior on boot CPU unplug 
still holds.

Thanks,

	Ingo
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