Messages in this thread |  | | | From | Chris Snook <> | | Date | Sat, 18 Jul 2009 23:00:55 -0400 | | Subject | Re: [RFC][PATCH] Introduce CLOCK_REALTIME_COARSE |
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On Fri, Jul 17, 2009 at 7:39 PM, john stultz<johnstul@us.ibm.com> wrote: > - if (likely(gtod->sysctl_enabled && gtod->clock.vread)) > + if (likely(gtod->sysctl_enabled))
This irks me. If the sysctl is enabled and the codepath is getting used often enough that we care about performance, branch prediction should do the right thing without compiler hints. On the other hand, if the sysctl is disabled, and the compiler is telling the cpu to ignore its branch predictor, it'll hurt. I don't think we should be wrapping (un)likely annotations around configuration options, unless we're biasing against debug conditions where we definitely don't care about performance. The patch is certainly no worse than the existing code, but while we have the hood up, it might be nice to remove the annotation, unless we're sure that it does no harm, and does some good.
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