Re: Pg+Linux swap use

Greg Stark wrote:
>
> William Yu <wyu@talisys.com> writes:
>
> > Rob Sell wrote:
> >
> > > Not being one to hijack threads, but I haven't heard of this performance hit
> > > when using HT, I have what should all rights be a pretty fast server, dual
> > > 2.4 Xeons with HT 205gb raid 5 array, 1 gig of memory. And it is only 50% as
> > > fast as my old server which was a dual AMD MP 1400's with a 45gb raid 5
> > > array and 1gb of ram.
> >
> > Not to get into a big Intel vs AMD argument but 50% sounds about right. Let's
> > first assume that the QS rating for the MP1400 is relatively accurate and
> > convert that to a 1.4GHz Xeon. 2.4/1.4 = +71%. Since processor performance
> > does not increase linearly with clockspeed, 50% is in line with expectations.
>
> Hm. You've read "50% as fast" as "50% faster".
> I wonder which the original poster intended.

Hyper-threading makes 2 cpus be 4 cpu's, but the 4 cpu's are each only
70% as fast, so HT is taking 2x cpus and making it 4x0.70 cpu's, which
gives 2.80 cpu's, and you get that only if you are hammering all four
cpu's with a full load.  Imagine ifd get two cpu-bound processes on the
first die (first 2 cpu's of 4) and the other CPU die is idle, and you
can see that HT isn't all that useful unless you are sure to keep all 4
cpu's busy.

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