Messages in this thread | | | Date | Thu, 17 Oct 2013 11:27:13 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 6/7] arm64, jump label: optimize jump label implementation |
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On Thu, 17 Oct 2013 22:40:32 +0800 Jiang Liu <liuj97@gmail.com> wrote:
> >>> You could make the code more concise by limiting your patching ability to > >>> branch immediates. Then a nop is simply a branch to the next instruction (I > >>> doubt any modern CPUs will choke on this, whereas the architecture requires > >>> a NOP to take time). > >> I guess a NOP should be more effecient than a "B #4" on real CPUs:) > > > > Well, I was actually questioning that. A NOP *has* to take time (the > > architecture prevents implementations from discaring it) whereas a static, > > unconditional branch will likely be discarded early on by CPUs with even > > simple branch prediction logic. > I naively thought "NOP" is cheaper than a "B" :( > Will use a "B #1" to replace "NOP". >
Really?? What's the purpose of a NOP then? It seems to me that an architecture is broken if a NOP is slower than a static branch.
-- Steve
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