Re: [PATCH] /sched/core: Fix Unixbench spawn test regression

Dietmar Eggemann
2025-03-10T15:29:18Z

On 10/03/2025 14:59, Vincent Guittot wrote:
> On Thu, 6 Mar 2025 at 17:26, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>
>> Hagar reported a 30% drop in UnixBench spawn test with commit
>> eff6c8ce8d4d ("sched/core: Reduce cost of sched_move_task when config
>> autogroup") on a m6g.xlarge AWS EC2 instance with 4 vCPUs and 16 GiB RAM
>> (aarch64) (single level MC sched domain) [1].
>>
>> There is an early bail from sched_move_task() if p->sched_task_group is
>> equal to p's 'cpu cgroup' (sched_get_task_group()). E.g. both are
>> pointing to taskgroup '/user.slice/user-1000.slice/session-1.scope'
>> (Ubuntu '22.04.5 LTS').
>
> Isn't this same use case that has been used by commit eff6c8ce8d4d to
> show the benefit of adding the test if ((group ==
> tsk->sched_task_group) ?
> Adding Wuchi who added the condition

IMHO, UnixBench spawn reports a performance number according to how many
tasks could be spawned whereas, IIUC, commit eff6c8ce8d4d was reporting
the time spend in sched_move_task(). …