hyperthreading on 2.6

on March 22, 2004 - 5:34pm

Linux kernel

I was wondering about the stability of hyperthreading on 2.6. Is this considered a very stable feature at this point? Redhat seems to claim their backported 2.6 code in their Enteprise server still has advantages over what resides in the 2.6 kernel today and just wondering if there is any validity to that.

thanks
kernelman99

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Works fine with a 2.4c@3.2 on

Anonymous

March 22, 2004 - 5:49pm

Works fine with a 2.4c@3.2 on an Abit IS7 over here.

Hyperthread scheduler

Con Kolivas

March 23, 2004 - 2:16am

Enabling SMP gets you most of the hyperthread benefits anyway, but you can improve things further with a hyperthread-aware scheduler. Only the recent -mm kernels treat hyperthread cpus specially.

hyperthread scheduler

kernelman99

March 23, 2004 - 10:04am

Is this hyperthread scheduler slated to be put into the stable kernel at any time or only in the -mm branch?

Anyone know of any benchmarks of the -mm kernel on a hyperthreaded machine versus a 2.6.4 kernel with SMP enabled just to see if there is truly a worthwhile advantage?

thanks
kernelman99

Benchmarks

Con Kolivas

March 23, 2004 - 10:18am

This scheduler will almost certainly be put into mainline. There are plenty of benchmarks on the linux kernel mailing list. Basically the benefit gets larger the more HT cpus you are running. However if you are running on a home desktop single HT processor and run things at different "nice" levels you will derive great benefit from this because it includes my SMT nice optimisation (see this website for details).

.config options

kernelman99

March 23, 2004 - 5:18pm

Do you need to set MPENTIUM4=y in order to see these added benefits on a HT system?

SCHED_SMT

Con Kolivas

March 23, 2004 - 6:32pm

To get the added benefits you need to enable the
[*] Symmetric multi-processing support
[*] SMT (Hyperthreading) scheduler support (NEW)
Setting mpentium4=y gives other minor benefits too, separate from these. I don't think they've been extensively measured but some preliminary measurements show this definitely helps too.

SMT ?

kernelman99

March 24, 2004 - 2:36pm

hmm. i dont seem to see [*] SMT (Hyperthreading) anywhere in the 2.6.4 config file. Is it under Processer Type And Features ?

Extra patches

Con Kolivas

March 26, 2004 - 10:15pm

No, as I said earlier to get this extra support you need to be using a non mainline kernel as this isn't merged into mainline yet. -mm, -ck and -wolk have it.