On 9/4/2023 2:23 PM, Peter Zijlstra wrote:
On Wed, Aug 30, 2023 at 10:42:39AM -0700, Elliot Berman wrote:
Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks.
If the task was running before entering TASK_FROZEN state
(__refrigerator()) or if the task received a wake up for the saved
state, then the task is woken on thaw. saved_state from PREEMPT_RT locks
can be re-used because freezer would not stomp on the rtlock wait flow:
TASK_RTLOCK_WAIT isn't considered freezable.
You don't actually assert that anywhere I think, so the moment someone
makes that happen you crash and burn.
I can certainly add an assertion on the freezer side.
Also:
-#ifdef CONFIG_PREEMPT_RT
+#if IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_FREEZER)
That makes wakeup more horrible for everyone :/
I don't think the hot wakeup path is significantly impacted because the
added checks come after the hot path is already not taken.
wait_task_inactive() is impacted in the case of contention on pi_lock,
but I don't think that is part of any hot path.
I'll run some further tests on my end to be sure about the wake up
latency. Are there any benchmarks/tests you like for measuring the hot
path? I can run those as well.
Thanks,
Elliot
