Messages in this thread | | | Date | Thu, 10 Jun 2010 20:52:07 -0400 | From | Jason Baron <> | Subject | Re: [PATCH 03/13] jump label v9: x86 support |
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On Thu, Jun 10, 2010 at 12:13:39PM -0400, Mathieu Desnoyers wrote: > * Jason Baron (jbaron@redhat.com) wrote: > > On Thu, Jun 10, 2010 at 02:14:40PM +0200, Ingo Molnar wrote: > > > * Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > On Wed, 2010-06-09 at 17:39 -0400, Jason Baron wrote: > > > > > + select HAVE_ARCH_JUMP_LABEL if !CC_OPTIMIZE_FOR_SIZE > > > > > > > > That deserves a comment somewhere, it basically makes OPTIMIZE_FOR_SIZE > > > > useless... > > > > > > Hm, we need more than a comment for that - distros enable CC_OPTIMIZE_FOR_SIZE > > > all the time, for the massive kernel image (and hotpath cache footprint) > > > savings. Is this fixable? > > > > > > Thanks, > > > > > > Ingo > > > > > > > When I tested 'jump label' with CC_OPTIMIZE_FOR_SIZE, I saw a small > > performance drop , b/c there is less block re-ordering happening. > > Is this a performance drop compared to a jump-label-less kernel or > compared to -O2 kernel compiled with jump labels ? Or both ? > > Mathieu >
Hi Mathieu,
So I'm quoting tbench benchmark here. The performance drop was jump label vs. all jump label patches backed out on -Os. If we move to -02, both the no jump label patches and the jump label patches applied are faster than all jump label patches backed out on -Os.
so:
jump labels -02 > no jump labels -02 > no jump labels -0s > jump lables -Os
thanks,
-Jason
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