Langsdorf, Mark wrote:
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?
If I'm understanding the question right, the contested
spin locks are being held for 5K to 10K iterations of PAUSE.
So 10K to 30K cycles if your estimate of the spinlock
cycle time is correct.
My estimate is not very reliable. Can you measure this?
btw, I'd expect you'd get much more significant improvement on Windows.
Booting 16-vcpu Windows 2008 x64 took forever on my dual core host, and
my guess is spinlock contention. Of course you'd need a working yield,
as Ingo said schedule() does very little.
--
error compiling committee.c: too many arguments to function
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