On 05/29/20 11:21, Mel Gorman wrote: > 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. Indeed. > > > 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 So you never had the TASK_GROUP part enabled when you noticed the regression? Or is it the other way around, you just disabled CONFIG_UCLAMP_TASK_GROUP to 'fix' it? Thanks -- Qais Yousef
