[linux-audio-dev] latency and P4 hyperthreading?

[Taybin Rutkin]

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


>