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vmx: reduce cpu load by eliminating nop-loop

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Sacrifice some of the sub-millisecond timer precision in favor of less
cpu load when the timer is about to be kicked a bit early.  Result is
visible *especially* when the guest idling.

Timer proc *still* has to send to the channel (in order to kick PIT
and RTC logic), which takes time, and compensates a bit for possibly
early runs.
This commit is contained in:
Sigrid 2021-02-23 15:54:09 +01:00
parent 007d42e741
commit 692919521c
1 changed files with 10 additions and 6 deletions
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16
sys/src/cmd/vmx/vmx.c
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@ -423,24 +423,28 @@ int timerid;
static void static void
sleeperproc(void *) sleeperproc(void *)
{ {
vlong then, now; vlong then, now, dt, adj;
timerid = threadid(); timerid = threadid();
timerevent = nanosec() + SleeperPoll; timerevent = nanosec() + SleeperPoll;
unlock(&timerlock); unlock(&timerlock);
threadsetname("sleeper"); threadsetname("sleeper");
adj = 0;
for(;;){ for(;;){
lock(&timerlock); lock(&timerlock);
then = timerevent; then = timerevent;
now = nanosec(); now = nanosec();
if(then <= now) timerevent = now + SleeperPoll; if(then <= now) timerevent = now + SleeperPoll;
unlock(&timerlock); unlock(&timerlock);
if(then - now >= MinSleep){ if(then > now){
sleep((then - now) / MSEC); dt = then - now;
continue; if(dt+adj >= MinSleep){
sleep((dt + adj) / MSEC);
continue;
}
adj = dt;
} }
while(nanosec() < then)
;
sendul(sleepch, 0); sendul(sleepch, 0);
} }
} }