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