[Xen-devel] Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 10/04/2011 09:30 AM, H. Peter Anvin wrote:
> On 10/04/2011 07:10 AM, Jason Baron wrote:
>> 1) The jmp +0, is a 'safe' no-op that I know is going to initially
>> boot for all x86. I'm not sure if there is a 5-byte nop that works on
>> all x86 variants - but by using jmp +0, we make it much easier to debug
>> cases where we may be using broken no-ops.
>>
> There are *plenty*.  jmp+0 is about as pessimal as you can get.

As an aside, do you know if a 2-byte unconditional jmp is any more
efficient than 5-byte, aside from just being a smaller instruction and
taking less icache?

    J

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