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SubjectRe: [PATCH v2 02/10] freezer: skip waking up tasks with PF_FREEZER_SKIP set
On Wed, May 01, 2013 at 06:35:00PM -0700, Colin Cross wrote:
> Android goes through suspend/resume very often (every few seconds when
> on a busy wifi network with the screen off), and a significant portion
> of the energy used to go in and out of suspend is spent in the
> freezer. If a task has called freezer_do_not_count(), don't bother
> waking it up. If it happens to wake up later it will call
> freezer_count() and immediately enter the refrigerator.
>
> Combined with patches to convert freezable helpers to use
> freezer_do_not_count() and convert common sites where idle userspace
> tasks are blocked to use the freezable helpers, this reduces the
> time and energy required to suspend and resume.
>
> Signed-off-by: Colin Cross <ccross@android.com>
> ---
> v2: move check to freeze_task()
>
> kernel/freezer.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index c38893b..8b2afc1 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -110,6 +110,18 @@ bool freeze_task(struct task_struct *p)
> {
> unsigned long flags;
>
> + /*
> + * This check can race with freezer_do_not_count, but worst case that
> + * will result in an extra wakeup being sent to the task. It does not
> + * race with freezer_count(), the barriers in freezer_count() and
> + * freezer_should_skip() ensure that either freezer_count() sees
> + * freezing == true in try_to_freeze() and freezes, or
> + * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
> + * normally.
> + */
> + if (freezer_should_skip(p))
> + return false;

Maybe a line or two explaining that this matters for power saving?
Other than that,

Acked-by: Tejun Heo <tj@kernel.org>

Oleg, this looks correct to me. Can you please ack too?

Thanks.

--
tejun


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