From: "Derrick, Jonathan" <jonathan.derrick@intel.com>
To: "dhowells@redhat.com" <dhowells@redhat.com>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Parallel compilation performance regression
Date: Thu, 18 Jun 2020 23:52:55 +0000 [thread overview]
Message-ID: <a1bafab884bb60250840a8721b78f4b5d3a6c2ed.camel@intel.com> (raw)
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
next reply other threads:[~2020-06-18 23:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-18 23:52 Derrick, Jonathan [this message]
2020-06-19 1:05 ` Parallel compilation performance regression Matthew Wilcox
2020-06-19 14:59 ` Derrick, Jonathan
2020-06-20 7:44 ` Sedat Dilek
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