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

[John Baldwin]

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).

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