Re: linux-oracle-hyper threading

No, there's more than just separate registers (and interrupts) per logical CPU.
When you got two threads running, they can for example share the same resources of a physical CPU. When one thread is doing a long latency operation, such as read from memory, other thread can use CPU to do it's tasks. Or when one thread is doing FPU operations, other one can execute "standard" operations. But this kind of context switching which is done in CPU, is done in thread level only, IIRC. But since Oracle in Linux (and Unixes) is using process based architecture, I don't thing we get any benefit from HT. Maybe in WindowsXP (2000 doesn't support HT), but anyway, since a typical Oracle instance doesn't that much of FPUs, MMX'es or whatever special units, it might be that HT doesn't give us anything at all.

Tanel.

"dick" <dick_at_dick.com> wrote in message
news:j1bTa.44889$PD3.4478394_at_nnrp1.uunet.ca...
> Intel's Hyper threading is simply a marketing feature. The only technology
> involved is adding a second set of registers to a single core. Hence you
now
> have 1 compute engine attempting to execute 2 instructions streams. Both
> instruction streams share the same cache, memory bus, execute engine
leading
> to increased contention, not increased performance. Hence you get 1/2 the
> cpu power each. The "context switching" is done at the chip level, not the
> OS level. hence the OS can not benefit from it. The only way
hyperthreading
> could provide any benefit would be if your OS was crafty enough to
allocate
> a totoally compute bound thread (no memory/disk access) with a non compute
> bound thread. We have disabled hyperthreading in BIOS and have seen huge
> performance increases in our compute bound activitites (20 seconds goes
down
> to 15 seconds).
>
>
> "Tanel Poder" <tanel@@peldik.com> wrote in message
> news:3f1d36ec$1_1_at_news.estpak.ee...
> > Hi!
> >
> > At least Redhat Advanced Server 2.1 sees hyperthreaded processors, that
a
> > 4way SMP box is actually seen as 8way.
> > But I wouldn't recommend using Oracle's parallel featres with 1 CPU
> machine
> > with hyperthreading, because parallel execution needs quite much
> > coordinating between slaves etc so you can make your processes even
slower
> > than with serial execution.
> >
> > Hyperthreading doesn't make 2 CPUs of one, it just allows us to use CPU
> > strength better with (quite a) few tricks.
> >
> > Tanel.
> >
> > "kshathrya" <kshathrya_at_hotmail.com> wrote in message
> > news:StBSa.107361$ye4.78464_at_sccrnsc01...
> > > hi all,
> > > does red hat linux 9 support hyperthreaded p4 systems?
> > > if i install oracle 9i on a rehat linux 9 hyperthreaded system, can i
> see
> > > that as 2 virtual processor from oracle's perspective?
> > > can i use oraclel's parallel features with these virtual processor?
> > >
> > > tnx,
> > > ks
> > >
> > >
> >
> >
>
>
Received on Wed Jul 23 2003 - 12:06:08 CDT