Re: [PATCH v3 6/7] arm64, jump label: optimize jump labelimplementation

[Will Deacon]

On Wed, Oct 16, 2013 at 06:11:45PM +0100, Jiang Liu wrote:
> On 10/16/2013 07:46 PM, Will Deacon wrote:
> > 
> >> +	} else {
> >> +		insn = aarch64_insn_gen_nop();
> > 
> > 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.

Will
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