Re: [PATCH 1/3] sched/wait: use freezable_schedule when possible

[Hugo Lefeuvre <hle@owl.eu.com>]

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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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