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SubjectRe: [PATCH 09/10] sched/fair: disable stealing if too many NUMA nodes
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On 10/22/2018 2:47 PM, Steven Sistare wrote:
> On 10/22/2018 1:06 PM, Peter Zijlstra wrote:
>> On Mon, Oct 22, 2018 at 07:59:40AM -0700, Steve Sistare wrote:
>>> The STEAL feature causes regressions on hackbench on larger NUMA systems,
>>> so disable it on systems with more than sched_steal_node_limit nodes
>>> (default 2).
>>
>> How come? From a quick read the stealing is per LLC, where do we steal
>> across nodes?
>
> See the complete explanation in this patch. It is deeper than can be gleaned
> from a quick read.

I should have said a bit more. Your quick take on stealing is correct, we do
not steal across nodes. However, stealing reduces average run queue length which
influences wake_affine migrations. Now see the complete explanation.

- Steve


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