Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and SPECjvm2008 benchmarks against 4.6 kernel

[Jirka Hladky]

Hello,

we see performance drop 30-40% for SPECjbb2005 and SPECjvm2008
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)

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?

Thanks a lot!
Jirka