Valgrind can run multi-threaded processes, but can only run one thread
at the same time.
So, when running a single process under Valgrind on a multi-cpu system,
you will not use more than 1 CPU
at the same time. This explains the 12.5% (1/8) that you have observed.
Note that this "serialised thread running" can somewhat badly interact
with CPU frequency scaling
and/or can give unfair scheduling of the threads in the process.
(see bug https://bugs.kde.org/show_bug.cgi?id=270006
<https://bugs.kde.org/show_bug.cgi?id=270006> )
Philippe
________________________________
From: Roman Biesiada [mailto:[email protected]]
Sent: Friday 2 December 2011 14:26
To: [email protected]
Subject: [Valgrind-users] How to boost application under
Callgrind control?
Hello,
I hope i did not send it twice :-)
I am trying to profile my own ldapd process with the use of
callgrind. I am running my software on quite powerful machine equipped
with 2 x E5440 @ 2.83GHz CPU. So I have total of 8 CPU cores that I can
use. Normally under heavy load my ldapd process takes ~ 400 % of CPU (4
full cores utilized for handling ldap requests). My ldapd is
multi-threaded daemon. When I run however ldapd under control of
valgrind/callgrind I can utilize only 12.5% of CPU (roughly 1/8 of CPU
power). I suspected that it is because only one of 8 cores was used by
valgrind/callgind. When I checked however CPU usage then "sar -P ALL"
command showed all cores were used equally. I thought that maybe
"--separate-threads=yes" switch could help but it didn't.
I am using callgrind-0.10.1-1.i586.rpm on SLES 9 sp4.
I am calling callgrind by:
valgrind --tool=callgrind /bin/ldapd &
Can anybody provide any hint how to use valgrind/callgrind to be
able to use my whole server capacity and simulate larger load for the
process being controlled by callgrind?
Thanks,
Roman
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