Re: Dual Xeon + HW RAID question

> > I missed your orig. post, but AFAIK multiprocessing kernels will handle
HT
> > CPUs as 2 CPUs each. Thus, our dual Xeon 2.4 is recognized as 4 Xeon 2.4
> > CPUs.
> >
> > This way, I don't think HT would improve any single query (afaik no
postgres
> > process uses more than one cpu), but overall multi-query performance has
to
> > improve.
>
> When you use hyperthreading, each virtual cpu runs at 70% of a full CPU,
> so hyperthreading could be slower than non-hyperthreading.  On a fully
> loaded dual cpu system, you are looking at 2.8 cpu's (0.70 * 4), while
> if it isn't loaded, you are looking at slowing down if you are only
> using 1 or 2 cpu's.

  Virtual cpus are not running at 70% of real cpus :). Slowdown will happen
if
scheduler will run 2 processes on the same real cpu. And I read that there
are
patches for Linux kernel to fix that. Sooner rather than later they will
appear
in Linus kernel.

  Mindaugas