Re: [Xen-devel] [PATCH 1/3] x86: use MOV instead of PUSH/POP when saving/restoring register state

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> 10/02/12 8:09 PM >>>
>On Tue, Oct 02, 2012 at 04:26:23PM +0100, Jan Beulich wrote:
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

>What's the reasoning behind it? Just that mov's are faster than
>pop/push?

No (that's not actually true anymore these days). The main reason is that with
MOV, part of the frame generation and register restoration can be more easily
skipped than when using PUSH/POP (would require extra stack pointer
adjustments on the alternative paths) - see patch 3.

Jan


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