Messages in this thread | | | Date | Tue, 01 Dec 2009 08:11:04 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC] [X86] Compile Option Os versus O2 on latest x86 platform |
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On 12/01/2009 02:14 AM, Arjan van de Ven wrote: > On Tue, 1 Dec 2009 16:54:04 +0800 > "Ma, Ling" <ling.ma@intel.com> wrote: > >> Hi Ingo >> >> Thanks for your correction, so we use perf stat --repeat 3 to test >> volano, tbench, and kbuild, Because netperf has multiple items we may >> send out later. > > a key question is.. how much more memory do you have free due to -Os? > (because memory is cache is performance on a system level as well) > and how much less icache pressure is there? >
From the re-run, it sounds like the only test that actually shows a significant difference is volano. From reading the numbers, it looks like the improvements are almost exclusively in IPC i.e. better scheduling -- all the other metrics are substantially worse; including a 10% increase in cache misses.
It would be interesting to see what functions are hot in volano. It might very well be that we could get a boost without significantly bloat the kernel as a whole by picking out a couple of hot object files and compiling those with -O2 or -O3.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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