Re: Hyper-Threading Vulnerability

[Grant Coady]

On Fri, 13 May 2005 14:49:25 -0400, Scott Robert Ladd <lkml@xxxxxxxxxxxxxxx> wrote:

>Alan Cox wrote:
>> HT for most users is pretty irrelevant, its a neat idea but the
>> benchmarks don't suggest its too big a hit
>
>On real-world applications, I haven't seen HT boost performance by more
>than 15% on a Pentium 4 -- and the usual gain is around 5%, if anything
>at all. HT is a nice idea, but I don't enable it on my systems.

P4-HT is great for winxp, a runaway process only gets half the CPU 
resources, keeps the system responsive.  I like HT for that reason, 
perhaps that's what it was designed for?  Hardware fix for msft 'OS' :o)

Recently on single AMD CPU box, 2.6.latest-mm, diff got stuck, no 
disk activity, 100% CPU, started another terminal, recompiled kernel 
with 8K stacks and rebooted, the whole time the unkillable 'diff' 
was using just over 1/2 of resources.  top showed all 1GB RAM in use, 
no swap activity, nothing odd in /proc/whatever -- only happened once.

I suspected 4k stacks as only change before 'crash' was turning on 
samba server day before, but I didn't trace 'problem' as it wasn't 
really a crash.  Impressive -- seeing 2.6 handling a stupid process, 
business as usual for everything else.  Haven't had a problem since 
changing to 8K stacks.  nfs, samba and ssh terminals on reiserfs 3.6
on via sata.  May have had nvidia driver installed at the time, I 
now load that only when X running (rare), mostly headless use.

--Grant.

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