Hi Scott,
Thanks for this work! I see significant improvement with my test code
(see below; obviously focussing quite specificially on one thing).
Before your diff (snapshot from a few days ago; OpenBSD 6.9-current
(GENERIC.MP) #1: Mon May 3 11:04:25 MDT 2021) I got:
[weerd@pom] $ ./measure
Running for 100 loops
timeout 800000us min/avg/max/std-dev: 800054/809727.250/810115/1609.611 us
timeout 400000us min/avg/max/std-dev: 409668/410000.406/410362/121.568 us
timeout 200000us min/avg/max/std-dev: 209421/209997.953/210553/97.505 us
timeout 100000us min/avg/max/std-dev: 109818/109997.078/110167/39.038 us
timeout 50000us min/avg/max/std-dev: 59887/59995.539/60108/27.651 us
timeout 25000us min/avg/max/std-dev: 29648/29993.961/30316/50.629 us
timeout 12500us min/avg/max/std-dev: 19910/19994.100/20098/24.265 us
timeout 6250us min/avg/max/std-dev: 19932/19994.020/20067/20.760 us
timeout 3125us min/avg/max/std-dev: 19806/19993.980/20221/33.121 us
timeout 1562us min/avg/max/std-dev: 19519/19993.971/20470/71.215 us
timeout 781us min/avg/max/std-dev: 19778/19993.980/20214/35.454 us
timeout 390us min/avg/max/std-dev: 19784/19994.029/20188/32.626 us
timeout 195us min/avg/max/std-dev: 19891/19994.230/20096/23.237 us
timeout 97us min/avg/max/std-dev: 19938/19994.170/20044/17.468 us
timeout 48us min/avg/max/std-dev: 19876/19994.010/20115/26.334 us
timeout 24us min/avg/max/std-dev: 19535/19994.199/20458/67.628 us
timeout 12us min/avg/max/std-dev: 19941/19994.240/20079/18.478 us
timeout 6us min/avg/max/std-dev: 19949/19994.150/20051/16.916 us
timeout 3us min/avg/max/std-dev: 19880/19994.221/20109/23.377 us
timeout 1us min/avg/max/std-dev: 19940/19994.289/20053/17.575 us
[I should add that these numbers are from an otherwise mostly idle
machine; they improved when my machine was busy building a new kernel]
After upgrading my local snap, cvs-up'ing, patching in your diff and
building + rebooting into a new kernel:
[weerd@pom] $ ./measure
Running for 100 loops
timeout 800000us min/avg/max/std-dev: 800041/808010.312/810021/2992.553 us
timeout 400000us min/avg/max/std-dev: 401639/402001.281/402373/-nan us
timeout 200000us min/avg/max/std-dev: 200959/200997.922/201041/-nan us
timeout 100000us min/avg/max/std-dev: 100456/100495.977/100533/37.185 us
timeout 50000us min/avg/max/std-dev: 50141/50244.809/50351/30.089 us
timeout 25000us min/avg/max/std-dev: 28917/30144.590/31396/175.702 us
timeout 12500us min/avg/max/std-dev: 20048/20094.420/20143/10.583 us
timeout 6250us min/avg/max/std-dev: 10016/10044.260/10084/9.683 us
timeout 3125us min/avg/max/std-dev: 9974/10044.060/10140/14.810 us
timeout 1562us min/avg/max/std-dev: 10016/10044.190/10078/6.827 us
timeout 781us min/avg/max/std-dev: 9964/10044.140/10143/14.516 us
timeout 390us min/avg/max/std-dev: 9578/10044.150/10507/66.234 us
timeout 195us min/avg/max/std-dev: 9981/10044.170/10122/16.570 us
timeout 97us min/avg/max/std-dev: 10010/10044.150/10117/10.721 us
timeout 48us min/avg/max/std-dev: 10004/10044.140/10083/10.331 us
timeout 24us min/avg/max/std-dev: 10016/10044.220/10078/6.487 us
timeout 12us min/avg/max/std-dev: 10014/10044.210/10079/6.802 us
timeout 6us min/avg/max/std-dev: 10013/10044.300/10085/9.871 us
timeout 3us min/avg/max/std-dev: 10007/10044.030/10090/8.477 us
timeout 1us min/avg/max/std-dev: 9980/10044.350/10135/13.301 us
(obviously some bug in the std-dev calculation there with the -nan)
Thanks again,
Paul
--- measure.c --------------------------------------------------------
#include <err.h>
#include <errno.h>
#include <math.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
#define LOOPCOUNT 100
volatile sig_atomic_t trigger;
void
sighdlr(int signum) {
trigger = signum;
}
int
main() {
int long long count, d, sum, min, max, tsumsq;
long timeout;
struct timeval str, end;
struct itimerval new_timer;
double avg, dev;
new_timer.it_interval.tv_sec = 0;
new_timer.it_interval.tv_usec = 0;
new_timer.it_value.tv_sec = 0;
signal(SIGALRM, sighdlr);
printf("Running for %d loops\n\n", LOOPCOUNT);
for (timeout = 800000; timeout != 0; timeout /= 2) {
new_timer.it_value.tv_usec = timeout;
min = 1000000000;
max = 0;
sum = 0;
tsumsq = 0;
for (count = 0; count != LOOPCOUNT; count++) {
trigger = 0;
setitimer(ITIMER_REAL, &new_timer, NULL);
gettimeofday(&str, NULL);
while (trigger == 0)
pause();
gettimeofday(&end, NULL);
d = (end.tv_sec - str.tv_sec) * 1000000 + \
end.tv_usec - str.tv_usec;
sum += d;
tsumsq += d * d;
if (d < min)
min = d;
if (d > max)
max = d;
}
avg = (float) sum / count;
dev = sqrt((float) tsumsq / count - avg * avg);
printf("timeout %7ldus min/avg/max/std-dev: %lld/%.3f/" \
"%lld/%.3f us\n", timeout, min, avg, max, dev);
}
}
----------------------------------------------------------------------
--
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