Bug 796297
| Summary: | turn off CONFIG_CC_OPTIMIZE_FOR_SIZE | ||
|---|---|---|---|
| Product: | Red Hat Enterprise MRG | Reporter: | Clark Williams <williams> |
| Component: | realtime-kernel | Assignee: | John Kacur <jkacur> |
| Status: | CLOSED ERRATA | QA Contact: | David Sommerseth <davids> |
| Severity: | medium | Docs Contact: | |
| Priority: | unspecified | ||
| Version: | 2.1 | CC: | bhu, lgoncalv, ovasik, srostedt |
| Target Milestone: | 2.1.5 | ||
| Target Release: | --- | ||
| Hardware: | x86_64 | ||
| OS: | Linux | ||
| Whiteboard: | |||
| 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
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | 2012-04-18 20:04:04 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
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Description
Clark Williams
2012-02-22 16:18:59 UTC
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
Technical note added. If any revisions are required, please edit the "Technical Notes" field
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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
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 |