On Tue, Aug 6, 2024 at 8:13 PM Suleiman Souhlal <suleiman@xxxxxxxxxx> wrote: > > When steal time exceeds the measured delta when updating clock_task, we > currently try to catch up the excess in future updates. > However, this results in inaccurate run times for the future clock_task > measurements, as they end up getting additional steal time that did not > actually happen, from the previous excess steal time being paid back. > > For example, suppose a task in a VM runs for 10ms and had 15ms of steal > time reported while it ran. clock_task rightly doesn't advance. Then, a > different task runs on the same rq for 10ms without any time stolen. > Because of the current catch up mechanism, clock_sched inaccurately ends > up advancing by only 5ms instead of 10ms even though there wasn't any > actual time stolen. The second task is getting charged for less time > than it ran, even though it didn't deserve it. > In other words, tasks can end up getting more run time than they should > actually get. > > So, we instead don't make future updates pay back past excess stolen time. > > Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx> Gentle ping. -- Suleiman
