question re klp_transition_work kickoff timeout

[Alexey Dobriyan <adobriyan@xxxxxxxxx>]

Hi, Josh.

I've been profiling how much time livepatching takes and I have a question
regarding these lines:

	void klp_try_complete_transition(void)
	{
		...
		if (!complete) {
			schedule_delayed_work(&klp_transition_work, round_jiffies_relative(HZ));
			return;
		}

	}

The problem here is that if the system is idle, then the previous loop
checking idle tasks will reliably sets "complete = false" and then
patching wastes time waiting for next second so that klp_transition_work
will repeat the same code without reentering itself.

I've created trivial patch which changes 2 functions and it takes
~1.3 seconds to complete transition:

	[   33.829506] livepatch: 'main': starting patching transition
	[   35.190721] livepatch: 'main': patching complete

I don't know what's the correct timeout to retry transition work
but it can be made near-instant:

	[  100.930758] livepatch: 'main': starting patching transition
	[  100.956190] livepatch: 'main': patching complete


	Alexey (CloudLinux)


--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -435,8 +435,7 @@ void klp_try_complete_transition(void)
 		 * later and/or wait for other methods like kernel exit
 		 * switching.
 		 */
-		schedule_delayed_work(&klp_transition_work,
-				      round_jiffies_relative(HZ));
+		schedule_delayed_work(&klp_transition_work, msecs_to_jiffies(1));
 		return;
 	}