On Sun, 2013-05-05 at 09:44 +0200, Jean Delvare wrote:
Reviving an old thread...
Le Tuesday 10 July 2012 à 05:42 +0200, Mike Galbraith a écrit :
On Mon, 2012-07-09 at 15:24 -0400, Jeff Mahoney wrote:
On 7/9/12 3:07 PM, Jean Delvare wrote:
Le lundi 09 juillet 2012 à 10:44 -0400, Jeff Mahoney a écrit :
On 7/9/12 10:37 AM, Jean Delvare wrote:
So, unless someone objects by then, I'll set CONFIG_CC_STACKPROTECTOR=y in i386 and x86_64 kernels tomorrow.
Thanks for looking into this, Jean. Since we don't have a bnc in the commit log to see what the performance degradation looked like originally, I'd like to see some analysis now to actually confirm whether it makes a difference anymore.
openSUSE 12.2 was supposed to be released in two days time but was delayed due to too much churn (among other things). If there is a performance difference, I'd prefer to know about it before we do the change rather than depend on post-release bug reports and the accompanying hand-wringing over whether to revert it.
Are you simply suggesting that I should change the configuration for master only and not the openSUSE-12.2 branch? Or should I wait even for master?
I admit I'm not sure how to test for performance regression. With CONFIG_CC_STACKPROTECTOR_ALL it was relatively obvious, but now that only selected functions get the protection, I can imagine that the performance hit completely depends on the drivers, filesystem etc. in use.
A quick look makes it seem like it really only has an effect during context switch.
Mike - What would you use to test this?
A pinned fork()/sched_yield() pair for pure context switch.
I have absolutely no idea how I would actually test that in practice, sorry.
I measured tbench, sched_yield and AIM7 compute on monteverdi with 3.9.0, and see diddly spit difference outside boot to boot and build to build variance.
OTOH I looked at Fedora [1], Red Hat [2], Slackware [3], Debian [4] and Ubuntu [5], they all have CONFIG_CC_STACKPROTECTOR=y. I can't imagine everyone else would have enabled this option if it caused a significant performance hit.
So I'm going to enable this option in the Factory kernel right now, on all architectures which support it.
[1] http://archive.fedoraproject.org/pub/fedora/linux/releases/18/Fedora/source/... [2] http://ftp.redhat.com/pub/redhat/linux/enterprise/6Server/en/os/SRPMS/kernel... [3] http://mirrors.dotsrc.org/slackware/slackware/source/k/config-x86/ [4] http://ftp.de.debian.org/debian/pool/main/l/linux/linux_3.2.41-2.debian.tar.... [5] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/369152
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