Bug 952422 - sysconf(_SC_NPROCESSORS_ONLN) performance problem
Summary: sysconf(_SC_NPROCESSORS_ONLN) performance problem
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: glibc
Version: 6.5
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Siddhesh Poyarekar
QA Contact: Arjun Shankar
Depends On:
TreeView+ depends on / blocked
Reported: 2013-04-15 23:19 UTC by Jacob Hunt
Modified: 2018-12-03 18:41 UTC (History)
7 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
This update improves performance of repeated calls of the sysconf function for getting values of _SC_NPROCESSORS_ONLN by caching the value for approximately a second. This could improve performance of some applications that use QReadWriteLocks in the Qt library or any other functionality that involves repeatedly getting the value for _SC_NPROCESSORS_ONLN.
Clone Of:
Last Closed: 2013-11-21 10:45:08 UTC

Attachments (Terms of Use)
Candidate fix (3.04 KB, patch)
2013-05-29 06:01 UTC, Siddhesh Poyarekar
no flags Details | Diff

System ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2013:1605 normal SHIPPED_LIVE Moderate: glibc security, bug fix, and enhancement update 2013-11-20 21:54:09 UTC

Description Jacob Hunt 2013-04-15 23:19:45 UTC
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):

Additional info:
This has been discussed upstream: 

Comment 11 Siddhesh Poyarekar 2013-05-29 06:01:42 UTC
Created attachment 754181 [details]
Candidate fix

Comment 14 errata-xmlrpc 2013-11-21 10:45:08 UTC
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.


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