Re: [rfc patch] i386: don't save eflags on task switch

Benjamin LaHaise
2006-11-05T03:56:15Z

On Sat, Nov 04, 2006 at 11:09:42AM -0800, Zachary Amsden wrote:
> Every processor I've ever measured it on, popf is slower. On P4, for
> example, pushf is 6 cycles, and popf is 54. On Opteron, it is 2 / 12.
> On Xeon, it is 7 / 91.

pushf has to wait until all flag dependancies can be resolved. On the
P4 with >100 instructions in flight, that can take a long time. Popf
on the other hand has no dependancies on outstanding instructions as it
resets the machine state.

-ben
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