rwatson at FreeBSD.org
Sat Jun 4 20:02:19 GMT 2005
On Thu, 2 Jun 2005, Singh, Vijay wrote:
> Hello, I am trying to run network benchmarking using netperf. I have a
> snapshot of "systat -vmstat 1". Is it OK to see those large number of
> interrupts (~ 1998) for the lapics?
That's a property of the increase in HZ to 1000 from 100, and that on 6.x,
each lapic generates HZ interrupts/sec to the individual processors,
rather than the programmable timer deliverable at HZ to a particular (or
round-robin'd) CPU, then that CPU broadcasting the clock tick to the other
CPUs using IPIs. The rate you see should be approximately HZ * #cpus, so
about 2000 for a dual-processor system (which is indeed about 1998).
While lowering HZ will lower the overhead associated with processing timer
ticks, it will also reduce timer granularity, which can affect performance
in other ways (for example, TCP may behave better with finer granularity
One of the things we don't show in vmstat -systat that we probably should
is per-CPU IPI rates. I've CC'd John in the hopes of convincing him to
add that to his todo list :-).
Robert N M Watson
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