>>>>> "LT" == Linus Torvalds <[email protected]> writes:
LT> 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.
LT> In fact, I think this is it!
LT> The load average is not calculated every tick, because that's not just
LT> expensive, but we also want to have some time-based decay. So it's
LT> calculated every LOAD_FREQ ticks.
LT> And guess what: LOAD_FREQ is defined to be exactly five seconds.
LT> So imagine if the timer gets to be in sync with another event that happens
LT> every five seconds - let's pick at random a 5-second JBD transaction
LT> thing?
LT> Anders - does this idiotic patch make a difference for you?
Yes, it does, it fixes the load average!!! I guess we have something
here!
Why does this problem only show up on my computer? Any idea?
/ Anders
LT> Without this, I can easily imagine that the rounding code tends to try to
LT> round to an even second, and the load-average code generally also runs at
LT> even seconds!
LT> Linus
LT> ---
LT> include/linux/sched.h | 2 +-
LT> 1 files changed, 1 insertions(+), 1 deletions(-)
LT> diff --git a/include/linux/sched.h b/include/linux/sched.h
LT> index a01ac6d..643de0f 100644
LT> --- a/include/linux/sched.h
LT> +++ b/include/linux/sched.h
LT> @@ -113,7 +113,7 @@ extern unsigned long avenrun[]; /* Load averages */
LT> #define FSHIFT 11 /* nr of bits of precision */
LT> #define FIXED_1 (1<<FSHIFT) /* 1.0 as fixed-point */
LT> -#define LOAD_FREQ (5*HZ) /* 5 sec intervals */
LT> +#define LOAD_FREQ (5*HZ+1) /* ~5 sec intervals */
LT> #define EXP_1 1884 /* 1/exp(5sec/1min) as fixed-point */
LT> #define EXP_5 2014 /* 1/exp(5sec/5min) */
LT> #define EXP_15 2037 /* 1/exp(5sec/15min) */
-
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