SMP causes weird performance problems
markus.kovero at multiwise.fi
Tue Oct 18 14:11:59 PDT 2005
Hi everyone, basically I've encountered very strange (for me atleast)
performance problem while tuning Dell Poweredge 1800.
I got 4-disk RAID5 set with harware controller made by Adaptec (works
with aac) and everything is fine until I recompile kernel with SMP support.
There are 2x Xeon CPU's with hyperthreading enabled (tried htt disabled
too) but after SMP turned on disk reads are affected somehow and reads
drop 320-350MB/s (with small files <1GB) to 110-150MB/s.
Disk writes slow down 1-2MB/s but thats acceptable for me.
Mainly I played around with dd but investigated it with bonnie++ too and
noticed same behaviour.
After that, removed RAID5 array, tried RAID10 (no win) and then even
with single volumes. No help, disk reads slow down dramatically after
turning SMP on.
There's no problem whatsoever SMP turned on or not in linux, reads and
writes are snappy. I just don't want linux. Ever. Again. (guys easily
drawn into flame wars dont read that last one:)
I've tried FreeBSD 5.4 and 6.0_BETA5, with and without adaptive_giant (I
read it may cause great slowdowns).
Any ideas, suggestions..?
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