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scx: Update conditions for WAKE_SYNC migration #167

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Mar 28, 2024
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scx: Update conditions for WAKE_SYNC migration #167

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14 changes: 10 additions & 4 deletions kernel/sched/ext.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2084,12 +2084,18 @@ static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
}

/*
* If WAKE_SYNC and the machine isn't fully saturated, wake up @p to the
* local DSQ of the waker.
* If WAKE_SYNC, the waker's local DSQ is empty, and the system is
* under utilized, wake up @p to the local DSQ of the waker. Checking
* only for an empty local DSQ is insufficient as it could give the
* wakee an unfair advantage when the system is oversaturated.
* Checking only for the presence of idle CPUs is also insufficient as
* the local DSQ of the waker could have tasks piled up on it even if
* there is an idle core elsewhere on the system.
*/
cpu = smp_processor_id();
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Oh, also, what does this relocation do?

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@Byte-Lab Byte-Lab Mar 28, 2024 •
edited
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We need it for the cpu_rq(cpu) call. Maybe it's a bit better to just use this_rq()?

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Oh, I mean, moving it out is completely fine. I just missed where it's used.

if ((wake_flags & SCX_WAKE_SYNC) && p->nr_cpus_allowed > 1 &&
!cpumask_empty(idle_masks.cpu) && !(current->flags & PF_EXITING)) {
cpu = smp_processor_id();
!cpumask_empty(idle_masks.cpu) && !(current->flags & PF_EXITING) &&
cpu_rq(cpu)->scx.local_dsq.nr == 0) {
if (cpumask_test_cpu(cpu, p->cpus_ptr))
goto cpu_found;
}
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