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SubjectRe: [RFC PATCH 7/9] sched: search SMT before LLC domain
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On 9/5/19 2:31 AM, Peter Zijlstra wrote:
> On Fri, Aug 30, 2019 at 10:49:42AM -0700, subhra mazumdar wrote:
>> Search SMT siblings before all CPUs in LLC domain for idle CPU. This helps
>> in L1 cache locality.
>> ---
>> kernel/sched/fair.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 8856503..94dd4a32 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6274,11 +6274,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>> return i;
>> }
>>
>> - i = select_idle_cpu(p, sd, target);
>> + i = select_idle_smt(p, target);
>> if ((unsigned)i < nr_cpumask_bits)
>> return i;
>>
>> - i = select_idle_smt(p, target);
>> + i = select_idle_cpu(p, sd, target);
>> if ((unsigned)i < nr_cpumask_bits)
>> return i;
>>
> But it is absolutely conceptually wrong. An idle core is a much better
> target than an idle sibling.
This is select_idle_smt not select_idle_core.

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