ffulin
commented
11 months ago Thanks for reporting this issue.
There is a discussion about what seems to be a related problem/the same core problem of Intel CPUs with hybrid core architectures having scheduling issues resulting in poor performance, particularly on Windows 10: https://github.com/fastbuild/fastbuild/pull/995
In that thread, the conclusions so far seem to be: a) Windows 10 in particular has scheduling issues, either due to Windows 10 not correctly supporting those CPUs and/or lack of chipset driver support b) Even on Windows 11, use of all cores may not be desirable
The involvement of process priority you mention is an interesting new piece of information (thanks again for reporting this)
My thoughts in general are:
- it'd be ideal if we can come up with a solution that works automatically, without the need for additional command line args. This could be via detection of OS version and/or hybrid core architectures if needed (hybrid core detection logic was recently added). If that's not possible or we need to expose control over conflicting but desirable behaviors, a command line arg and/or options exposed in the Settings() would be fairly reasonable.
- it may be time to re-evaluate setting "below normal" priority. The original intent for this was to keep PCs interactive during compiles, but while it did help when it was added (circa Windows 7) it a) might not be needed anymore or b) might actually be causing more problems than it solves (given what you've reported). I'd be open to potentially getting rid of this entirely (or based on Windows version perhaps)
Out of interest, do you have any Windows 11 machines of this configuration, and if so, do they exhibit different/improved scheduling behavior?
kuznetsoveugeneskyboxlabs
mwl4
On modern Intel processors (Tested with i7-13700K) with Windows 10, I encounter the issue where FastBuild does not utilize all of the CPU cores (only 8 out of 24 available). This is an unfavorable interaction between how the Windows scheduler works with processes with Below-Normal priority which FBuild uses. Unfortunately, that is not good enough for our use case and we would like to max out the work initiator CPU to accelerate the build process.
This is how CPU utilization looks when running on Below-Normal process priority for FastBuild, not great!
I confirmed that setting a priority of FBuild to Normal resolves this issue and all cores are being utilized in this case. Thus I have a feature that I would like to propose (and I am already working on a PR) you as a user of FastBuild will be able to set the priority of the processes being spawned using a command line.
By default, you keep a Below-Normal with an option to bump it to Normal for this kind of edge case. (Windows only)
For reference, Incredibuild also has this type of an issue but it allows configurable process priority for its workers. In case you set it to Normal then it will mitigate this problem.
I wonder if this is a noticed issue and/or if anything has been done/proposed to address it? Any input is also appreciated!