Yet another bugfix release for MuQSS and the -ck patchset with one of the most substantial latency fixes yet. Everyone should upgrade if they're on a previous 4.8 patchset of mine. Sorry about the frequency of these releases but I just can't allow a known buggy release be the latest version.
MuQSS by itself for 4.8:
MuQSS by itself for 4.7:
I'm hoping this is the release that allows me to not push any more -ck versions out till 4.9 is released since it addresses all remaining issues that I know about.
A lingering bug that has been troubling me for some time was leading to occasional massive latencies and thanks to some detective work by Serge Belyshev I was able to narrow it down to a single line fix which dramatically improves worst case latency when measured. Throughput is virtually unchanged. The flow-on effect to other areas was also apparent with sometimes unused CPU cycles and weird stalls on some workloads.
Sched_yield was reverted to the old BFS mechanism again which GPU drivers prefer but it wasn't working previously on MuQSS because of the first bug. The difference is substantial now and drivers (such as nvidia proprietary) and apps that use it a lot (such as the folding @ home client) behave much better now.
The late introduced bugs that got into ck3/muqss115 were reverted.
The results come up quite well now with interbench (my latency under load benchmark) which I have recently updated and should now give sensible values:
If you're baffled by interbench results, the most important number is %deadlines met which should be as close to 100% as possible followed by max latency which should be as low as possible for each section. In the near future I'll announce an official new release version.
Pedro in the comments section previously was using runqlat from bcc tools to test latencies as well, but after some investigation it became clear to me that the tool was buggy and did not work properly with bfs/muqss either so I've provided a slightly updated version here which should work properly: