Initial 6.1 questions

Kris Kennaway kris at
Mon Jun 12 20:32:50 UTC 2006

On Mon, Jun 12, 2006 at 09:08:12PM +0100, Robert Watson wrote:
> On Mon, 12 Jun 2006, Scott Long wrote:
> >I run a number of high-load production systems that do a lot of network 
> >and filesystem activity, all with HZ set to 100.  It has also been shown 
> >in the past that certain things in the network area where not fixed to 
> >deal with a high HZ value, so it's possible that it's even more 
> >stable/reliable with an HZ value of 100.
> >
> >My personal opinion is that HZ should gop back down to 100 in 7-CURRENT 
> >immediately, and only be incremented back up when/if it's proven to be the 
> >right thing to do. And, I say that as someone who (errantly) pushed for 
> >the increase to 1000 several years ago.
> I think it's probably a good idea to do it sooner rather than later.  It 
> may slightly negatively impact some services that rely on frequent timers 
> to do things like retransmit timing and the like.  But I haven't done any 
> measurements.

As you know, but for the benefit of the list, restoring HZ=100 is
often an important performance tweak on SMP systems with many CPUs
because of all the sched_lock activity from statclock/hardclock, which
scales with HZ and NCPUS.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url :

More information about the freebsd-performance mailing list