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SubjectRe: P4 Xeon summary inquiry
On Tue, 7 May 2002, Jesse Wyant wrote:

> 'make -j2 bzImage; make -j2 modules; make modules_install; sync'
> results in compile times around 3 minutes 45 seconds or so. With HT enabled,
> and using -j4 instead of -j2, my compile time comes down to around 2:57 or
> so--a significant improvement.
> However, 'dnetc's throughput in RC5 keys/s is much lower with HT enabled:
> it runs 4 clients, and each client chugs through about 720kKeys/s.
> With HT disabled, the two dnetc clients run through 2.8MKeys/s each. (So
> it's around half as fast with HT enabled!) When I'm finished downloading
> RedHat 7.3, I'll reboot into Hyperthreading-enabled mode, and run
> 'dnetc --benchmark' to confirm this.

We have found the same thing. If you are running single threaded, 2 or
less consecutive on a 2-proc system it's better to disable HT, however,
on a system which will have multiple runable processes looking for CPU
time concurrently, then using HT is a benefit.

We noticed ~2%-5% drop in single process performance with HT
enabled, but >20% with multiple processes with HT enabled.

Thing is, with 2 1.8 GHz CPUs, a 2% drop may be appreciable, but not
generally noticable overall.

The tests were done with a Dell PE4600 (2x1.8GHz, 2GB RAM), 2.4.18, with
Ingos' irqbalance-2.4.17-B1.patch and timer-irq-balance-2.4.18.patch.

The system is now in production with these patches and kernel, and has
been very stable (of course now it *will* crash).

James Bourne

> Haven't had a chance to benchmark more than that yet. But no gross issues
> when running with HT enabled. (Tribes2, Q3A and RTCW feel equally fast
> between the two configurations.)
> -jesse
> > I am trying to make a dual P4-Xeon box (P4DCE, Intel 869) work optimally.
> > After some search in list archives, I have found this points:
> >
> > - You need ACPI, and boot with acpismp=force, to have hyperthreading
> > (see 4 cpus)
> > - To balance interrupts, a patch from Ingo is needed
> > - To balance timers, one other patch was needed, but this in included
> > in 2.4.19-pre8 (do not know since which pre is there)
> >
> > I tried to boot with acpismp=force, but then performance was dog slow,
> > I could count lines scrolling on a rxvt.
> > I checked mtrr and look like working. Box has 1Gb of ram, so kernel
> > is using CONFIG_HIGHMEM4G=y.
> > Kernel is the standard highmem Mandrake kernel in 8.2
> > (2.4.18-6mdkenterprise) that is mainly a plain 2.4.18 with some
> > .19-pre1 fixes.
> >
> > Any correction ? Any known problem in 2.4.18 about this issue that
> > has bee corrected in pres for 19 ?
> >
> > Any idea about the performance loss ?
> >
> -
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James Bourne, Supervisor Data Centre Operations
Mount Royal College, Calgary, AB, CA

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