* Suleiman Souhlal <suleiman@xxxxxxxxxx> [2024-09-11 20:15:22]: > 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 things using > clock_task, as they end up getting additional steal time that did not > actually happen. > > 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 taks runs on the same rq for 10ms without any time stolen in > the host. > 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. > This can result in tasks 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> > --- > v2: > - Slightly changed to simply moving one line up instead of adding > new variable. > > v1: https://lore.kernel.org/lkml/20240806111157.1336532-1-suleiman@xxxxxxxxxx > --- After moving the line up, this looks good to me. Reviewed-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxx> -- Thanks and Regards Srikar Dronamraju
