linux-kernel - Re: [PATCH v2 2/2] nohz: make nohz

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Message-ID: <5525357B.2080205@ezchip.com>
Date:	Wed, 8 Apr 2015 10:04:43 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	"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 v2 2/2] nohz: make nohz_full imply isolcpus

On 04/08/2015 05:41 AM, Peter Zijlstra wrote:
> On Mon, Apr 06, 2015 at 02:16:45PM -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.
> So the Changelog and the patch don't seem to agree with one another.
>
> The Changelog states that nohz_full should depend on isolcpus.

The git commit message says "make nohz_full imply isolcpus".
That's consistent with the code.

> The patch implies nohz_full for isolcpus.
>
> These are not the same; and I don't see the argument for the former make
> sense for the latter.
>
> In specific isolcpus without nohz_full does make sense.
>
>> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
>> Acked-by: Mike Galbraith <umgwanakikbuti@...il.com> ["thumbs up!"]
>> Acked-by: Rik van Riel <riel@...hat.com>
>> ---
>>   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();

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

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