Low performances with Pentium 4 cpu


I installed Suse 10.1 and root 5.12/00f (and previously 5.12/00a) on a computer with a single Pentium4 3.2 GHz processor. Everything seems to work, but when I run a simulation in root, cpu statistics report that the task uses just 50% of cpu maximum load. This impression is supported from the time needed to accomplish the task, which turn out to be about twice that required to run similar task on a computer with AMD 3200 64 bit single cpu processor.

I suspect that root is misled by Hyper-Threading tecnology, which emulates two cpus… any suggestion to run task with 100% of cpu maximum load?


No idea what is going on. I could understand to see only 50% load since ROOT runs as a single process and uses only one “processor”, but not when you run only half the expected performance (hyperthreading typically brings only 10-15% improvement when running multple jobs at the same time). Is it not that the CPU is two time slower then the AMD 64 one?

Cheers, Fons.

I try to make the same root task on three different computers:

  • my old office pc, with AMD duron @ 1,3 GHz, 512Mb RAM;
  • my home pc, with AMD 3200 64 bit processor (frequency 2.0 GHz), 2Gb RAM;
  • my new office pc, with P4 3,2 GHz, 2Gb RAM.

The task lasts 156, 92 and 149 seconds respectively: difference from 1.3 GHz processor and P4 3,2 GHz processor is negligible respect to the gain obtain with my home pc and so I deduced that something doesn’t work very well…


The P4 number looks indeed way to low. Did you monitor the system while running you ROOT job? Use top and xosview, maybe some resource is low due to something else.


[quote=“lksodt”]on a computer with a single Pentium4 3.2 GHz processor

Just to ask: You don’t have HT enabled with this processor, do you?

I made some tests.

First, I verified that no other processes were occupying CPU. Then I disabled HT support from bios: CPU is occupied at 100% during root simulation, but performance doesn’t change very much.

The most puzzling result is that, enabling HT, a single root task occupies 50% of CPU load, while two contemporary root tasks occupied 100% of CPU load. This is confirmed by time needed to accomplish the tasks, which in the former configuration (single task) is about 170s, while in the latter (two contemporary tasks) only 225s, i.e. less than that needed to accomplish two individually subsequent tasks.

I attach the command “top” output for the two cases: I note that user CPU load pass from a value of about 50% to almost 100%.

Thanks to all!

TopOutput.txt (1.86 KB)