Re: Execution times running multiple instances of an application
- From: Tim Prince <timothyprince@xxxxxxxxxxxxx>
- Date: Mon, 26 Nov 2007 19:23:51 -0800
Dr Ivan D. Reid wrote:
On Mon, 26 Nov 2007 12:55:56 -0500, deltaseq0 <deltaseq0@xxxxxxxxxx>As OP is running on a single core HyperThreaded processor, where both
wrote in <JMD2j.18$gL1.13@xxxxxxxxxxxx>:
I'm doing some testing of an application using a Pentium 4 HT cpu. The
application runs under Cygwin using the XWin X Server and an xterm window.
It takes 1.9 hrs to complete using gcc 4.2.1 configured with thread model:
single. When I look at Windows Task Manager, it shows a cpu usage of 50%
with no other apps running at the time. From a previous optimization thread,
I tried running 2 instances of the application at the same time by opening
up another window under XWin. Task manager shows 100% cpu usage but instead
of completing the 2 applications in 2 hours, it takes 3.9 hours; slightly
more than twice the time if I had run the applications sequentially. Was
this to be expected?
I have seen instances where a programme has completely slowed down
due to its "hopping" from one CPU to another and (presumably) losing its
cache in the process -- although this may have been on a proper dual-core
rather than a P4. You can check if it makes a difference in Task Manager --
in the Processes tab, right-click on the programme and select "Set Affinity"
from the drop-down menu. Set one copy of the programme to run on CPU 0
and the other to run on CPU 1 and see if it runs any faster.
jobs use the same L2 cache, the most likely cache problem is contention
for cache resource. Swapping L1 is not as big a problem.
My primary use for HyperThreading is running cygwin gcc/gfortran
testsuite, where most of the time is spent on the extremely slow disk
operations.
Under Windows, you are lucky if raising the task manager meter from 50%
to 100% gets you a 20% increase in throughput with HT. It may approach
50% increased throughput with a recent linux, in cases where your
application runs threads without much increase in memory requirement.
.
- References:
- Execution times running multiple instances of an application
- From: deltaseq0
- Re: Execution times running multiple instances of an application
- From: Dr Ivan D. Reid
- Execution times running multiple instances of an application
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