hyperthreading, nice level problem

rudi_m · 2006-09-23, 10:34

Hi,

I just benchmarked mprime again on a P4/HT with smp/smt kernel.
The results were as I expected - The "mprime throughput" is about 10% higher if I run 2 instances at the same time.

But by the way I noticed something odd:
If I run two mprimes at the same time - one with nice level 19 and one with 0 - then both instances are needing the same time per iteration.
So the nice mprime harms the other mprime - setting niceness becomes useless.

For me this seems to be logical on a HT CPU since the scheduler gives both active processes 100% of one CPU (which are only a virtual CPUs!).

My problem is clear now, even if I run only one nice mprime on that machine - it steals about 50% CPU time when another (more important) process becomes active.

Is there any solution for that exceptly disabling HT/smp?
My kernel is 2.6.13 - maybe the HT support improved since then?

For now I will play around with MaxLoad=1.5 in prime.ini but its not really satisfactory because mostly mprime is still not sleeping even another process is active since 1 or 2 minutes.

Mystwalker · 2006-09-23, 21:19

You can tell mprime* to stop computing once certain processes are running. AFAIK, the required option is in undoc.txt.

* Actually, I only know for sure that prime95 is capable of this, but I guess it's similar with mprime.

2006-09-23, 10:34	#1
rudi_m Jul 2005 2·7·13 Posts	hyperthreading, nice level problem Hi, I just benchmarked mprime again on a P4/HT with smp/smt kernel. The results were as I expected - The "mprime throughput" is about 10% higher if I run 2 instances at the same time. But by the way I noticed something odd: If I run two mprimes at the same time - one with nice level 19 and one with 0 - then both instances are needing the same time per iteration. So the nice mprime harms the other mprime - setting niceness becomes useless. For me this seems to be logical on a HT CPU since the scheduler gives both active processes 100% of one CPU (which are only a virtual CPUs!). My problem is clear now, even if I run only one nice mprime on that machine - it steals about 50% CPU time when another (more important) process becomes active. Is there any solution for that exceptly disabling HT/smp? My kernel is 2.6.13 - maybe the HT support improved since then? For now I will play around with MaxLoad=1.5 in prime.ini but its not really satisfactory because mostly mprime is still not sleeping even another process is active since 1 or 2 minutes. Last fiddled with by rudi_m on 2006-09-23 at 11:07

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Nice progress!	schickel	FactorDB	29	2012-07-18 17:03
Nice pic	Dubslow	Forum Feedback	0	2012-05-02 02:13
The Hello - I am - Nice to meet you thread....	Prime Monster	Lounge	23	2012-02-11 11:08
Let's do another nice big GNFS job!	fivemack	Factoring	84	2011-04-26 10:22
Nice link...	Xyzzy	Lounge	4	2003-06-28 13:37

2006-09-23, 21:19	#2
Mystwalker Jul 2004 Potsdam, Germany 831₁₀ Posts	You can tell mprime* to stop computing once certain processes are running. AFAIK, the required option is in undoc.txt. * Actually, I only know for sure that prime95 is capable of this, but I guess it's similar with mprime.