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Re: high sys time, very very slow builds on new 24-core system
On Wed, Mar 23, 2011 at 05:24:12PM -0400, Thor Lancelot Simon wrote:
> All cores spend well over 50% time in 'sys', even when all or almost
> all are running cc1 processes. The kernel is amd64 -current GENERIC
> from about 1 week ago -- no DIAGNOSTIC, DEBUG, KMEMSTATS, LOCKDEBUG,
I am getting some lockstat output now; I will send it here as soon as
I have it.
While I wait, I can see two very curious things in systat vmstat:
1) There is a truly huge number of zfod pages, sometimes well
over 100,000/sec, even with 10-15% CPU idle. I wonder if the
idle loop page zeroer is for some reason not working efficiently
on this system.
2) About 200 xfers/sec (about 3MB/sec worth) is still going on
to the SSD for much of the build process. It's all writes.
All build directories (obj, dest, tools, release) are on
a separate tmpfs, /tmp is on tmpfs, the machine isn't
using any swap, and I am building with -U -O. By the time I
verified all this, the disk writes were done so I couldn't
use fstat to see what files might be being written.
I wonder if some tool has reverted to using /var/tmp for its
intermediate files, or similar. Don't see an obvious
culprit for that, however.
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