performance degradation in 6.2 when adding a second quad core
kris at FreeBSD.org
Thu Feb 21 22:50:01 UTC 2008
benjamin thielsen wrote:
> hi folks-
> we've been experiencing some interesting behavior on single quad core
> computers as compared to dual quad core computers.
Yes, this can happen when you run into concurrency bottlenecks in the
application or in the kernel.
> it appears that adding a second processor to the system (leaving it
> otherwise untouched) actually decreases performance. we've got a small
> rudimentary test process, built in house, that does postgresql queries
> (selects) via http requests (apache2/php5).
7.0 will perform much better than 6.x on SMP workloads in general,
however TCP I/O is not yet at the point where it can make efficient use
of many processors (there has been a lot of work on TCP in 7.0, but it
is not yet at the stage where a performance payoff will be seen with
more than about 4 CPUs). This is one of the projects that we will be
working on this year, so you can expect future releases to have improved
concurrent TCP performance.
There may be other issues, so if you like you can enable LOCK_PROFILING
and obtain a trace when your workload is running (see the manpage). You
should also try the ULE scheduler on 7.0.
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