diff options
| -rw-r--r-- | sys/src/9/pc/main.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/sys/src/9/pc/main.c b/sys/src/9/pc/main.c index 7dbd9ad5e..bc12d5608 100644 --- a/sys/src/9/pc/main.c +++ b/sys/src/9/pc/main.c @@ -31,6 +31,7 @@ char *confval[MAXCONF]; int nconf; uchar *sp; /* user stack of init proc */ int delaylink; +int idle_spin; static void multibootargs(void) @@ -1083,6 +1084,15 @@ cistrncmp(char *a, char *b, int n) /* * put the processor in the halt state if we've no processes to run. * an interrupt will get us going again. + * + * halting in an smp system can result in a startup latency for + * processes that become ready. + * if idle_spin is zero, we care more about saving energy + * than reducing this latency. + * + * the performance loss with idle_spin == 0 seems to be slight + * and it reduces lock contention (thus system time and real time) + * on many-core systems with large values of NPROC. */ void idlehands(void) @@ -1093,4 +1103,6 @@ idlehands(void) halt(); else if(m->cpuidcx & Monitor) mwait(&nrdy); + else if(idle_spin == 0) + halt(); } |