sched/fair: Optimize select_idle_cpu
commit 60588bfa upstream. select_idle_cpu() will scan the LLC domain for idle CPUs, it's always expensive. so the next commit : 1ad3aaf3 ("sched/core: Implement new approach to scale select_idle_cpu()") introduces a way to limit how many CPUs we scan. But it consume some CPUs out of 'nr' that are not allowed for the task and thus waste our attempts. The function always return nr_cpumask_bits, and we can't find a CPU which our task is allowed to run. Cpumask may be too big, similar to select_idle_core(), use per_cpu_ptr 'select_idle_mask' to prevent stack overflow. Fixes: 1ad3aaf3 ("sched/core: Implement new approach to scale select_idle_cpu()") Signed-off-by:Cheng Jian <cj.chengjian@huawei.com> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by:
Srikar Dronamraju <srikar@linux.vnet.ibm.com> Reviewed-by:
Vincent Guittot <vincent.guittot@linaro.org> Reviewed-by:
Valentin Schneider <valentin.schneider@arm.com> Link: https://lkml.kernel.org/r/20191213024530.28052-1-cj.chengjian@huawei.com Signed-off-by:
Paul Gortmaker <paul.gortmaker@windriver.com>
parent
51fa438e
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