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SubjectRe: [PATCH 1/3] sched/wait: use freezable_schedule when possible
Hi,

> > The result is a potential performance gain during freeze, since less
> > tasks have to be awaken.
>
> I'm curious did you try the freezing process and see if pointless wakeups are
> reduced? That would be an added bonus if you did.

Test env: fresh Debian QEMU vm with 4.19 stable kernel.

Test process:

- Added two debug logs to freeze_task:

bool freeze_task(struct task_struct *p)
{
unsigned long flags;
[snip]
pr_info("freezing a task");
[snip]
if (freezer_should_skip(p)) {
pr_info("skeeping a task");
return false;
}
[snip]
}

- Triggered manual freeze:

# echo freezer > /sys/power/pm_test
# echo test_resume > /sys/power/disk
# echo disk > /sys/power/state

- grep -c to get the number of "freezing a task" and "skeeping a task"
lines in kern.log.

Results:

Without my patch: 448 calls freeze_task, 12 skipped.
With my patch: 448 calls, 32 skipped.

2.6x more tasks skipped.

Not sure this is the best way to test this patch, though. Any advice?

regards,
Hugo

--
Hugo Lefeuvre (hle) | www.owl.eu.com
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