Re: HyperThreading

[Saman Barghi <saman.b@xxxxxxxxx>]

Thomas, 

Thanks a lot for your response. I did build a custom kernel and ran the benchmarks again. The results are very promising, I did use the same settings as mentioned here. DFBSD is catching up with free bsd,  although it is a little bit behind. My only concern is that when there is 1 or 2 threads running DFBSD is far behind FBSD, but when it gets to 3 thread running the performance boosts up and beyond that it stays close to FBSD, is there any explanation for that !? 

What kind of machines are not supported for SMP !? I am just about to run some benchmarks on a 12 core 64 bit machine, it would be nice to know if it is not supported before I start. 

Btw, Do you guys have any specific benchmark in mind that might worth trying ?! 

Cheers,

Saman

http://cs.uwaterloo.ca/~sbarghi 

On Thu, Feb 17, 2011 at 2:44 PM, Thomas Nikolajsen <thomas.nikolajsen@mail.dk> wrote:

>Since I moved from FreeBSD I make assumptions, I thought it is enabled by default which seems not to be case.

Well, you just did test which didn't show multithread speedup, this is indicates UP also.
'sysctl hw.ncpu' will show number of avail. CPUs (like in FreeBSD).

>I will build a custom kernel then (or is there a better way !? )

You will have to build a kernel; see build7) man page
(like in FreeBSD; major difference is we use /sys/config for KERNCONFs).

>But my question is, why UP is proffered over SMP ?! is there any specific reason !?

DragonFly SMP kernel doesn't yet run on all systems.

>Does DFBSD perform better in UP rather than SMP mode ?!

On UP system  (ncpu=1), I don't think you will notice difference in performance
between UP kernel and SMP kernel (I don't notice it at least);
DragonFly SMP performance is rather good, also on UP systems;
I didn't see benchmarks recently (lots of development is going on in this area);
you are very welcome to do benchmarks and publish results; Please include current master.

>I just read that UP is the default mode forever (http://www.shiningsilence.com/dbsdlog/2010/10/26/6670.html),
>it is interesting to know the reason though.

As noted above SMP kernel won't run on all systems yet.

 -thomas