wastedcores

Since the article is more than 5 years old, it would be interesting to find out what became of their efforts. The GitHub repo linked in the article (https://github.com/jplozi/wastedcores) was last active in December 2017, and apparently contains some bugfixes, however with the caveat "The provided patches fix the issues encountered with our workloads, but they are not intended as generic bug fixes. They may have unwanted side effects and result in performance loss or energy waste on your machine." Did this result in any scheduling bugfixes that actually made it into the Linux kernel?

This article is from ~april 2016, the last commit was on may 2016 [1] [1] https://github.com/jplozi/wastedcores

Run "numastat". If you only see one "node" column, then these issues don't affect you. At Netflix, almost all our systems are single NUMA node. I tested the patches on 1 and 2 node NUMA, and saw 0% performance improvements, for some simple workloads. The paper is also uninformed about scheduler bugs in general. Yes, there have been lots of scheduler bugs (I've worked on more in other kernels too, not Linux, where scheduling is even worse!). Yes, we already have tools for diagnosing them (eg, examining run queue latency as a histogram). Yes, we've already used visualizations too. There's information for reproducing the bugs here: https://github.com/jplozi/wastedcores/issues/1 . If you think for a second that you've hit these bugs, you should read these steps.

"Cores may stay idle for seconds while ready threads are waiting in runqueues." I do not believe it, sorry. Troll paper. Check out the massive indentation change in this patch which obscures the changes being made: https://github.com/jplozi/wastedcores/blob/master/patches/sc... Good grief.

The last paragraph of that segment says they pick it because it's the first in the list of idle cores. E.g. if a core is no longer idle it removes itself from the list, and it adds itself at the end, so effectively it's ordered in deminishing idletime time. Though from my understanding of the patch they walk over all CPUs which is not precisely constant time, and it doesn't seem to be just the list of idle CPUs; for_each_online_cpu(_cpu): https://github.com/jplozi/wastedcores/blob/master/patches/ov... That said from what I grasp of the code it also doesn't bail out when power management is enabled, so maybe the public code or the paper are not at the same stage of development.

As indicated in the paper, patches (currently for kernel 4.1) are here: https://github.com/jplozi/wastedcores