Re: [performance bug] kernel building regression on 64 LCPUs machine

[Jeff Moyer <jmoyer@redhat.com>]

Hi, Jan,

So, the results are in.  The test workload is an fs_mark process writing
out 64k files and fsyncing each file after it's written.  Concurrently
with this is a fio job running a buffered sequential reader (bsr).  Each
data point is the average of 10 runs, after throwing out the first run.
File system mount options are left at their defaults, which means that
barriers are on.  The storage is an HP EVA, connected to the host via a
single 4Gb FC path.

ext3 looks marginally better with your patches.  We get better files/sec
AND better throughput from the buffered reader.  For ext4, the results
are less encouraging.  We see a drop in files/sec, and an increase in
throughput for the sequential reader.  So, the fsync-ing is being
starved a bit more than before.

        ||       ext3        ||       ext4        ||
        || fs_mark | fio bsr || fs_mark | fio bsr ||
--------++---------+---------++---------+---------||
vanilla || 517.535 | 178187  || 408.547 | 277130  ||
patched || 540.34  | 182312  || 342.813 | 294655  ||
====================================================
%diff   ||  +4.4% |    +2.3% ||  -16.1% |  +6.3%  ||

I'm tired right now, but I'll have a look at your ext4 patch in the
morning and see if I can come up with a good reason for this drop.

Let me know if you have any questions.

Cheers,
Jeff