Messages in this thread | | | Date | Fri, 8 Aug 2008 13:36:46 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 0/5] ftrace: to kill a daemon |
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On Fri, 8 Aug 2008, Mathieu Desnoyers wrote: > * Steven Rostedt (rostedt@goodmis.org) wrote: > > > > I originally used jumps instead of nops, but unfortunately, they actually > > hurt performance more than adding nops. Ingo told me it was probably due > > to using up the jump predictions of the CPU. > > > > Hrm, are you sure you use a single 5-bytes nop instruction then, or do > you use a mix of various nop sizes (add_nops) on some architectures ?
I use (for x86) what is in include/asm-x86/nops.h depending on what the cpuid gives us.
> > You can consume the branch prediction buffers for conditional branches, > but I doubt static jumps have this impact ? I don't see what "jump > predictions" you are referring to here exactly.
I don't know the details, but we definitely saw a drop in preformance between using nops and static jumps.
-- Steve
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