Andi Kleen wrote:
For me, when compiled with -O2, it results in
84
88
132
which basically says: a "rdtsc->rdtsc" is 84 cycles, putting a "pushfl" in
between is another _4_ cycles, and putting a "popfl" in between is about
another 48 cycles.
This means we should definitely change restore_flags() to only STI,
never popf
sti is expensive as well; iirc just as expensive on most processors as
popf, although I don't have hard numbers to back this up on hand. An
_unlikely_ jcc + popf? is better than a sti, for sure, but a likely
jcc+popf could cost more than a jcc+sti, depending on model.
Zach
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