Ingo Molnar wrote:
* Avi Kivity <avi@xxxxxxxxxx> wrote:
I.e. the 3000 cycles value itself could be eliminated as well.
(with just a common-sense max of say 100,000 cycles enforced)
Yeah, though that has a much smaller effect as it's only
responsible for a few microseconds of spinning.
3000 cycles would be 1-2 usecs. Isnt the VM exit+entry cost still in
that range?
It's 3000 executions of rep nop, so you need to account for the entire
spinlock loop body.
The Linux spinlock is
"1:\t"
"cmpl %0, %2\n\t"
"je 2f\n\t"
"rep ; nop\n\t"
"movzwl %1, %2\n\t"
/* don't need lfence here, because loads are in-order */
"jmp 1b\n"
5 instructions, maybe 2-3 cycles, not counting any special rep nop
overhead. Mark, any idea what the spin time is?
VM entry/exit is around 1us on the newer processors.
--
error compiling committee.c: too many arguments to function
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