Ok, I've done a more comprehensive test. TU = getuid() syscall test.
This is on a 2xCPU SMP box.
With one process running the syscall is 34 nS faster with the
new critical_*(). With two processes running the syscall is
41 nS faster with the new critical_*().
So, not 300nS, but not too shabby. I expect we'll add another 15-20nS
of performance later on when the routines are inlined and the sysctl
instrumentation is removed. As I said, cli and sti (and the pushfl/popl
combination) are nasty instructions. This test is with a 1.1GHz P3
but I believe it is even worse on a P4.
-Matt
pid 204 guid/sec 813324 One TU running, old critical_*()
pid 204 guid/sec 813336 1.230 uS/call
pid 204 guid/sec 813513
pid 204 guid/sec 813394
pid 204 guid/sec 813099
pid 204 guid/sec 836959 new critical_*()
pid 204 guid/sec 836779 1.195 us/call --> 34 nS
pid 204 guid/sec 836939
pid 214 guid/sec 687816 Two TU's running, old critical_*()
pid 214 guid/sec 687632 1.454 uS/call
pid 214 guid/sec 687857
pid 214 guid/sec 687887
pid 214 guid/sec 667454 new critical_*()
pid 214 guid/sec 667562 1.496 uS/call --> 41 nS
pid 214 guid/sec 668551
pid 214 guid/sec 668686
pid 214 guid/sec 668789
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