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Subject: [Bug 173541] load average 0.60 at 100% idle
Date: Tue, 27 Oct 2015 08:33:02 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=173541

--- Comment #9 from Alexander Motin <mav@FreeBSD.org> ---
I don't know whether it is the only cause of such behavior, but I have one
logical explanation.  The problem goes from the sampled nature of our load
average calculation.  To reduce power usage new clock code tries to aggregate
events in bursts to reduce number of CPU wakeups.  As result, if system is
idle, its CPU may wakeup as low as two times per second.  And if that CPU has
some other events waking it up, it is quite likely they will be aggregated with
load average sampling.  As result, there is high enough probability that
sampler will see some "load" to account, while it has no idea that that load
will disappear in microsecond for another second.  Enabling periodic interrupts
breaks the event aliasing -- load average sampling will more likely fire in
moments when system is really idle.  But do we want to consume several extra
watts of power just for one good looking number?  To solve this we should
probably change our mechanism of load average calculation somehow.  If anybody
have ideas -- I am all ears.

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