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Bug 796297 - turn off CONFIG_CC_OPTIMIZE_FOR_SIZE
turn off CONFIG_CC_OPTIMIZE_FOR_SIZE
Status: CLOSED ERRATA
Product: Red Hat Enterprise MRG
Classification: Red Hat
Component: realtime-kernel (Show other bugs)
2.1
x86_64 Linux
unspecified Severity medium
: 2.1.5
: ---
Assigned To: John Kacur
David Sommerseth
:
Depends On:
Blocks:
  Show dependency tree / graph
 
Reported: 2012-02-22 11:18 EST by Clark Williams
Modified: 2016-05-22 19:34 EDT (History)
4 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
* Cause: CONFIG_CC_OPTIMIZE_FOR_SIZE set with assumption that smaller code would yield hot cache lines and good performance * Consequence: this config caused gcc to generate jump-to-jump code which causes cache line bouncing, hurting performance * Fix: turn off CONFIG_CC_OPTIMIZE_FOR_SIZE * Result:slightly larger kernel but better cache utilization
Story Points: ---
Clone Of:
Environment:
Last Closed: 2012-04-18 16:04:04 EDT
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
CRM:
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2012:0496 normal SHIPPED_LIVE Red Hat Enterprise MRG Realtime 2.1 kernel bug fix update 2012-04-18 20:01:52 EDT

  None (edit)
Description Clark Williams 2012-02-22 11:18:59 EST 
Description of problem:

Originally this config was set with the assumption that smaller code size would yield hot cache lines and faster code, but that has not been shown to occur.
Comment 3 David Sommerseth 2012-04-04 09:04:34 EDT 
Verified through config review.

# grep CONFIG_CC_OPTIMIZE_FOR_SIZE /boot/config-3.0.*
/boot/config-3.0.18-rt34.53.el6rt.x86_64:CONFIG_CC_OPTIMIZE_FOR_SIZE=y
/boot/config-3.0.25-rt44.57.el6rt.x86_64:# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
#

CONFIG_CC_OPTIMIZE_FOR_SIZE is removed in the new kernel
 -> VERIFIED
Comment 4 Clark Williams 2012-04-11 11:08:21 EDT 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
* Cause: CONFIG_CC_OPTIMIZE_FOR_SIZE set with assumption that smaller code would yield hot cache lines and good performance
* Consequence: this config caused gcc to generate jump-to-jump code which causes cache line bouncing, hurting performance
* Fix: turn off CONFIG_CC_OPTIMIZE_FOR_SIZE
* Result:slightly larger kernel but better cache utilization
Comment 5 errata-xmlrpc 2012-04-18 16:04:04 EDT 
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/RHBA-2012-0496.html
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