linux-kernel - Re: [PATCH 2/2] nohz: make nohz

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Date:	Fri, 3 Apr 2015 15:20:20 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>
CC:	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] nohz: make nohz_full imply isolcpus

On 04/03/2015 01:42 PM, Frederic Weisbecker wrote:
> On Fri, Apr 03, 2015 at 12:24:08PM -0400, cmetcalf@...hip.com wrote:
>> From: Chris Metcalf <cmetcalf@...hip.com>
>>
>> It's not clear that nohz_full is useful without isolcpus also
>> set, since otherwise the scheduler has to run periodically to
>> try to determine whether to steal work from other cores.
>>
>> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> I think Rick has a similar patch.

I didn't see anything relevant in linux-next, though I did see 
cpu_isolated_map
made into a public symbol in a recent commit by Rik.

Rik, what's the change you're proposing that's similar to this one? Thanks!

>> ---
>> I am puzzled why this has not been done before, so I suspect
>> there is some argument against it that I am missing, but I
>> wasn't able to turn anything up by searching LKML.
>>
>>   kernel/sched/core.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index f0f831e8a345..275f12c608f2 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -6836,6 +6836,7 @@ static int init_sched_domains(const struct cpumask *cpu_map)
>>   	doms_cur = alloc_sched_domains(ndoms_cur);
>>   	if (!doms_cur)
>>   		doms_cur = &fallback_doms;
>> +	tick_nohz_full_set_cpus(cpu_isolated_map);
>>   	cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map);
>>   	err = build_sched_domains(doms_cur[0], NULL);
>>   	register_sched_domain_sysctl();
>> -- 
>> 2.1.2
>>

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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