On Thu, Jun 16, 2016 at 06:38:50PM +0200, Jirka Hladky wrote: > Hello, > > we see performance drop 30-40% for SPECjbb2005 and SPECjvm2008
Blergh, of course I don't have those.. :/ > benchmarks starting from 4.7.0-0.rc0 kernel compared to 4.6 kernel. > > We have tested kernels 4.7.0-0.rc1 and 4.7.0-0.rc3 and these are as > well affected. > > We have observed the drop on variety of different x86_64 servers with > different configuration (different CPU models, RAM sizes, both with > Hyper Threading ON and OFF, different NUMA configurations (2 and 4 > NUMA nodes) What kind of config and userspace setup? Do you run this cruft in a cgroup of sorts? If so, does it change anything if you run it in the root cgroup? > Linpack and Stream benchmarks do not show any performance drop. > > The performance drop increases with higher number of threads. The > maximum number of threads in each benchmark is the same as number of > CPUs. > > We have opened a BZ to track the progress: > https://bugzilla.kernel.org/show_bug.cgi?id=120481 > > You can find more details along with graphs and tables there. > > Do you have any hints which commit should we try to reverse? There were only 66 commits or so, and I think we can rule out the hotplug changes, which should reduce it even further. You could see what the parent of this one does: 2159197d6677 sched/core: Enable increased load resolution on 64-bit kernels If not that, maybe the parent of: c58d25f371f5 sched/fair: Move record_wakee() After that I suppose you'll have to go bisect.
