Messages in this thread | | | From | "Derrick, Jonathan" <> | Subject | Parallel compilation performance regression | Date | Thu, 18 Jun 2020 23:52:55 +0000 |
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Hi David,
I've been experiencing a performance regression when running a parallel compilation (eg, make -j72) on recent kernels.
I bisected it to this commit:
commit b667b867344301e24f21d4a4c844675ff61d89e1 Author: David Howells <dhowells@redhat.com> Date: Tue Sep 24 16:09:04 2019 +0100
pipe: Advance tail pointer inside of wait spinlock in pipe_read() Advance the pipe ring tail pointer inside of wait spinlock in pipe_read() so that the pipe can be written into with kernel notifications from contexts where pipe->mutex cannot be taken.
Prior to this commit I got 70% or so thread saturation of cc1 and after it rarely gets above 15% and would often drop down to 1-2 threads. It doesn't look like a clean revert either. Looking at upstream, it seems that some later code changed the wakeup. I'm not really sure how this all fits into parallelized make.
Best Jon
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