Re: [PATCH v6 3/5] sched: Enforce user requested affinity

From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH v6 3/5] sched: Enforce user requested affinity
Date: Wed, 31 Aug 2022 16:48:51 -0400	[thread overview]
Message-ID: <9ccb1100-295e-a99b-949b-a400f177c947@redhat.com> (raw)
In-Reply-To: <Yw8nXttOnNjK/1y4@hirez.programming.kicks-ass.net>


On 8/31/22 05:18, Peter Zijlstra wrote:
> On Thu, Aug 25, 2022 at 09:01:17PM -0400, Waiman Long wrote:
>
>> @@ -9352,6 +9381,11 @@ int sched_cpu_activate(unsigned int cpu)
>>   		sched_update_numa(cpu, true);
>>   		sched_domains_numa_masks_set(cpu);
>>   		cpuset_cpu_active();
>> +		/*
>> +		 * Preallocated scratch cpumask
>> +		 */
>> +		if (!rq->scratch_mask)
>> +			rq->scratch_mask = kmalloc(cpumask_size(), GFP_KERNEL);
>>   	}
> this is too late; I think you'll have to add a sched_cpu_prepare() and
> simply fail the cpu-up when the allocation fails.
>
That is the reason why I have a fallback allocation in 
__set_cpus_allowed_ptr(). Thanks for the suggestion, I will looking into 
doing that.

Cheers,
Longman