cvs commit: src/sys/sys time.h src/sys/kern kern_time.c
rwatson at FreeBSD.org
Sun Nov 27 10:03:58 GMT 2005
On Sun, 27 Nov 2005, Poul-Henning Kamp wrote:
> In message <200511270055.jAR0tIkF032480 at repoman.freebsd.org>, Robert Watson writes:
>> This offers a minimum update rate of 1/HZ,
>> but in practice will often be more frequent due to the frequency of
>> time stamping in the kernel:
> Not quite...
> The precision is guaranteed to be no worse than 1msec, and is unlikely
> to be significantly better.
Sadly, for some workloads it will be -- we update the cached time stamp
for every kernel context switch, so workloads that trigger lots of context
switches will also trigger time stamp updates. I.e., loopback network
traffic due to the netisr and user space context switches, high in-bound
network triffic due to ithread and netisr context switches, etc.
Robert N M Watson
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