cvs commit: src/sys/amd64/amd64 cpu_switch.S machdep.c

[John Baldwin]

On Thursday 20 October 2005 10:34 am, Scott Long wrote:
> John Baldwin wrote:
> > On Thursday 20 October 2005 01:45 am, Bruce Evans wrote:
> >>On Tue, 18 Oct 2005, Scott Long wrote:
> >>I use 100 and never downgraded to use 1000 except for testing how bad
> >>it is.  The default number is now up to <number of CPUs> * 2 * HZ.
> >>E.g., it is 4000 on sledge.freebsd.org.  While 4000 interrupts/sec can
> >>be handled easily by any new machine, 4000 is a disgustingly large
> >>number to use for clock interrupts.  Have a look at vmstat -i output
> >>on almost any machine.  On most machines in the freebsd cluster, the
> >>total number of interrupts is dominated by clock interrupts even with
> >>HZ = 100.
> >
> > Note that on 4.x you don't get to see the interrupt counts for the hz +
> > stathz * (cpus - 1) IPIs for all the clock interrupts, so in real
> > numbers, each CPU has gone from hz + stathz to hz * 2 interrupts. 
> > However, the higher number is offset by the fact that the interrupt
> > handler for the lapic case doesn't have to touch any hardware, and it
> > also works much more reliably (getting irq0 to work in APIC mode on some
> > amd64 nvidia chipsets required several quirks, and future motherboards
> > will probably continue to require quirks since Windows uses the APIC
> > timer in APIC mode and doesn't require irq0 to work in APIC mode).
>
> I'm in complete argreement that using the APIC timer is the right thing
> to do, and I believe that we did some tests to show that the high
> interrupt rate didn't have an appreciable effect on performance.
> However, I'd like to revisit the HZ=1000 decision for 7-CURRENT.
>
> Scott

Agreed.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org