[AMD64-SMP] I can't get my cpus working at 100%

[Josh Paetzel]

On Thursday 24 August 2006 13:09, Laurent C wrote:
> Hello all,
>
> I can't get my athlon x2 processor working at 100% on cpu-intensive
> apps. I've made some tests with "john --test" and "transcode", wich
> are both multithreaded apps.
>
> For example if I launch transcode it takes between 50% and 55% cpu
> (on top), and if I launch
> a second transcode session on another file, the total cpu used on
> top is 100%, without lower the speed
> of the first transcode session.
>
> The same behavior occurs with john. A single "john --test" give me
> some speed results, and the same
> command with a transcode or second "john --test" give me the same
> speed results but now with 100%
> cpu used.
>
> I made a "portupgrade -auf" just after building and installing my
> SMP kernel and World, to be sure all is up-to-date.
>
> So it's seems it's not a "top" output problem, but a real underuse
> of the computing power.
>
> %uname -a
> FreeBSD wks02.chez.oim 6.1-STABLE FreeBSD 6.1-STABLE #0: Thu Aug 17
> 18:47:31 CEST 2006    
> laurent at wks02.chez.oim:/usr/obj/usr/src/sys/WKS02_SMP  amd64
>
> Does anyone could explain me what's happening with my system ?

An application that is not written to take advantage of a multi-cpu 
system is unable to max out more than one CPU at a time.  top isn't 
really SMP 'aware' so in a dual CPU system something that is using 
50% of the CPU is in reality maxing one CPU.  This is a bit 
over-simplified because the process will bounce between the two CPUs 
but it will never execute on more than one at a time.

-- 
Thanks,

Josh Paetzel