On Thu, May 28, 2020 at 05:51:31PM +0100, Qais Yousef wrote: > > Indeed, that one. The fact that regular distros cannot enable this > > feature due to performance overhead is unfortunate. It means there is a > > lot less potential for this stuff. > > I had a humble try to catch the overhead but wasn't successful. The observation > wasn't missed by us too then. > As with all things, it's perfectly possible I was looking at a workload where the cost is more obvious but given that the functions are inlined, it's not trivial to spot. I just happened to spot it because I was paying close attention to try_to_wake_up() at the time. > On my Ubuntu 18.04 machine uclamp is enabled by default by the way. 5.3 kernel > though, so uclamp task group stuff not there yet. Should check how their server > distro looks like. > Elsewhere in the thread, I showed some results based on 5.7 so uclamp task group existed but I had it disabled. The uclamp related parts of the kconfig were # zgrep UCLAMP kconfig-5.7.0-rc7-with-clamp.txt.gz CONFIG_UCLAMP_TASK=y CONFIG_UCLAMP_BUCKETS_COUNT=5 # CONFIG_UCLAMP_TASK_GROUP is not set -- Mel Gorman SUSE Labs
