Subject: Re: [linux-audio-dev] latency and P4 hyperthreading?
From: Taybin Rutkin (taybin_AT_earthlink.net)
Date: Tue Jun 03 2003 - 14:14:44 EEST
How does the P4 machine compare against itself with hyperthreading turned off?
I'm not surprised that hyperthreading is slower than a true dual CPU setup. Two CPUs sharing their cache? That's got to increase cache misses.
Taybin
-------Original Message-------
From: Fernando Pablo Lopez-Lezcano <nando_AT_ccrma.Stanford.EDU>
Sent: 06/02/03 09:05 PM
To: linux-audio-dev_AT_music.columbia.edu
Subject: [linux-audio-dev] latency and P4 hyperthreading?
>
> Hi all, has anyone tested latency on a P4 machine with Hyperthreading
support? (HT simulates two processors on one processor using - I guess -
the spare time available in the cpu when it is waiting for, for example,
memory accesses).
Anyway, on a:
P4 2.4G 800MHz fsb, 875P chipset, 1G ram, Seagate Barracuda V 60G drive:
Booting into an smp kernel with HT enabled in the bios (kernel based on
2.4.21-rc6 with the usual low latency, preemptive and full acpi kernel
patches) I see both processors, but the latency in the disk tests (using
latencytest 0.42) has spikes that go up to 10/15 msecs, specially in the
read/write test.
If I boot into a up kernel, or if I boot with acpi=off I see only one
processor and the latency for the disk tests is fine.
Same kernel, same alsa on a dual Athlon MP 1800+ machine does not show
any abnormal latency behavior so this seems to be confined to HT
machines... :-(
I guess "made up" processors are not as good as real ones :-)
-- Fernando
>
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