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Description of problem:

We have an application that has a lot of threads and uses QReadWriteLocks to protect data that the threads are accessing. When our server is heavily loaded, the application spends about 60% of it's time in system time as opposed to user time. Further investigation showed that the QMutex class is calling sysconf(_SC_NPROCESSORS_ONLN) for each thread that tries to get a lock where that lock is already locked. Thus most of that system time is spent in this system call.

Version-Release number of selected component (if applicable):
glibc-2.12-1.107.el6.x86_64


Additional info:
This has been discussed upstream: 
http://sourceware.org/ml/libc-alpha/2011-06/msg00064.html

Created attachment 754181 [details]
Candidate fix

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-1605.html