On Wed, 3 Oct 2007, Chuck Ebbert wrote: > > But we reduce the number of samples because some ticks just never > happen when the timers get rounded: > > No rounding: > > tick ............... tick > 1 running 1 running > > Rounded: > > tick > 2 running > > In the first case the average is 1, but it's 2 in the second.
In fact, I think this is it! The load average is not calculated every tick, because that's not just expensive, but we also want to have some time-based decay. So it's calculated every LOAD_FREQ ticks. And guess what: LOAD_FREQ is defined to be exactly five seconds. So imagine if the timer gets to be in sync with another event that happens every five seconds - let's pick at random a 5-second JBD transaction thing? Anders - does this idiotic patch make a difference for you? Without this, I can easily imagine that the rounding code tends to try to round to an even second, and the load-average code generally also runs at even seconds! Linus --- include/linux/sched.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index a01ac6d..643de0f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -113,7 +113,7 @@ extern unsigned long avenrun[]; /* Load averages */ #define FSHIFT 11 /* nr of bits of precision */ #define FIXED_1 (1<<FSHIFT) /* 1.0 as fixed-point */ -#define LOAD_FREQ (5*HZ) /* 5 sec intervals */ +#define LOAD_FREQ (5*HZ+1) /* ~5 sec intervals */ #define EXP_1 1884 /* 1/exp(5sec/1min) as fixed-point */ #define EXP_5 2014 /* 1/exp(5sec/5min) */ #define EXP_15 2037 /* 1/exp(5sec/15min) */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/