Messages in this thread | | | Date | Tue, 24 Nov 2009 13:17:09 -0500 | Subject | Re: [PATCH 0/5] branch hint tweaks | From | Aaron Cohen <> |
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On Tue, Nov 24, 2009 at 12:50 PM, Brian Gerst <brgerst@gmail.com> wrote: > On Tue, Nov 24, 2009 at 5:54 AM, Tim Blechmann <tim@klingt.org> wrote: >> hi all, >> >> doing some branch hint profiling of 2.6.31 on my nehalem machine showed >> a few >> incorrect branch hints. >> these patches remove or change the branch hints > > I'm not sure what version of GCC added this, but I wonder if this > option will fix the problem: > > -fno-guess-branch-probability > Do not guess branch probabilities using heuristics. > > GCC will use heuristics to guess branch probabilities if they are > not provided by profiling feedback (-fprofile-arcs). These heuristics > are based on the control flow graph. If some branch probabilities are
Is the kernel's use of unlikely typically intended to mean "I consider the following unlikely so please optimize with that expectation" or is meant to indicate "the following is a slow-path so please pessimize it" or both? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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