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SubjectRe: Linux 2.4.19-rc3 (hyperthreading)
Date
I would caution against having hyperthreading on by default in the 2.4.19 
release. I am seeing a significant degrade in network workloads on P4 with
hyperthreading on. On 2.4.19-pre10, I get 788 Mbps on NetBench, but on
2.4.19-rc1 (and probably rc3, should know in an hour), I get 690 Mbps. It is
clearly a hyperthreading/interrupt routing issue. On this system (4 x P4),
with no hyperthreading, there is enough CPU to handle all interrupts on CPU0
(this is where all ints go by default). With hyperthreading on, I get "1/2"
of a CPU for interrupt processing. What ends up happenning is that CPU0 is
at 100%, while CPU1-CPU7 are at 75%. Now I know the "noth" is available, but
since hyperthreading is not proven to give a performance boost to more than
1/2 of the common workloads for linux users (or is it? who has done tests?),
I'd like to see this default behavior reversed, and still use acpismp=force
to enable hyperthreading.
Also, If anyone has performance results for their workloads showing a boost
with hyperthreading, I would really like to know.

-Andrew Theurer



<<So here goes rc3. Another -rc is going to come only in the case of really
critical problem(s).

I'm attaching the rc2->rc3 changelog only because the full changelog got
too big (I guess thats why my -rc2 announce mail didnt go to lk).>>


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