Re: comments about hardware
On Thu, 2005-07-21 at 16:13 -0400, Faheem Mitha wrote:
>
> On Thu, 21 Jul 2005, Lennart Sorensen wrote:
>
> > One dual core opteron compared to two single core opterons:
>
> > Each opteron has a memory controller built in that does dual channel
> > memory support. A dual core opteron still only has one memory
> > controller and hypertransport to the chipset. The two cores share it,
> > so two single cores have theoretically twice the memory bandwidth of a
> > single dual core. Of course they also require a dual socket board
> > rather than a single socket board, and you could put two dual core
> > opterons in a dual board and get to use 4 cores total without having to
> > pay for a much more expensive 4 socket board. Two cores in one package
> > may on the other hand have faster access to each other's caches which
> > may be an advantage in some situations, while in others sharing the
> > memory bandwidth could hurt. At the same time the dual core would
> > always have it's memory local, while two single cores half the ram is
> > likely connected to the other cpu so access would have a 1 cycle penalty
> > for access. A decent OS would try to make sure applications are running
> > on the cpu whos ram they are currently in whenever possible.
>
> Hi,
>
> Thanks for the information. If you have experience of using dual core
> processors with Debian, I'd be glad to hear of the details.
Well, I've Xeons in my box which support hyperthreading (HT). I presume
this is the same as "dual core". However, with a 2.4 debian SMP kernel I
found that for my applications it was better to turn HT off. I've yet to
try with 2.6 kernel but it is meant to have better scheduling. But as
implied above performance will depend on your applications!
Michael
PS: I read a lot of 2.4.xxx and 2.6.yyy but was there ever a 2.5.zzz?!
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