Date: Fri, 04 Dec 2009 15:52:39 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-hackers@freebsd.org Subject: Request for information - timers, hz, interrupts Message-ID: <hfb7ne$mi$1@ger.gmane.org>
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For a long time, at least in the 6-stable timeframe, I was used to
seeing timer interrupts going at the frequency of 2*HZ, e.g. this is
from 6.4-RELEASE:
kern.clockrate: { hz = 250, tick = 4000, profhz = 166, stathz = 33 }
debug.psm.hz: 20
cpu0: timer 6789885563 499
cpu2: timer 6789885538 499
cpu1: timer 6789885538 499
cpu3: timer 6789885537 499
Then sometime in 7.x this changed to 4*HZ, which continues in 8.x, e.g.
from 7.2-RELEASE:
kern.clockrate: { hz = 250, tick = 4000, profhz = 1000, stathz = 142 }
kern.hz: 250
cpu0: timer 1368329715 988
cpu1: timer 1368324640 988
cpu2: timer 1367642854 988
cpu3: timer 1367642874 988
I'm not very worried about it (though maybe laptop users might be
because of potential power drainage) but would like to know the
explanation behind it.
Presumably it has something to do with profhz but what and why? There
isn't an obvious correlation between profhz frequency in 6.x and HZ and
in 7.x. and HZ.
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