Sorry to reply to myself ... On Mon, 12 Jun 2006, Andrew R. Reiter wrote:
:On Tue, 13 Jun 2006, David Xu wrote: : ::On Tuesday 13 June 2006 04:32, Kris Kennaway wrote: ::> 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. ::> ::> Kris :: ::sched_lock is another big bottleneck, since if you 32 CPUs, in theory ::you have 32X context switch speed, but now it still has only 1X speed, ::and there are code abusing sched_lock, the M:N bits dynamically inserts ::a thread into thread list at context switch time, this is a bug, this ::causes thread list in a proc has to be protected by scheduler lock, ::and delivering a signal to process has to hold scheduler lock and ::find a thread, if the proc has many threads, this will introduce ::long scheduler latency, a proc lock is not enough to find a thread, ::this is a bug, there are other code abusing scheduler lock which ::really can use its own lock. :: ::David Xu : :Given that it seems that various scenarios for locking bottlenecks can :occur on various systems with different numbers of CPUs. Has there been :any research done on providing "best fit" profiles for varied N cpu :systems? Meaning at compile time certain profiles are taken for a given system to provide a good effort at providing a "best fit" for locking with their system. : :Cheers, :Andrew : :-- :[EMAIL PROTECTED] :_______________________________________________ :freebsd-performance@freebsd.org mailing list :http://lists.freebsd.org/mailman/listinfo/freebsd-performance :To unsubscribe, send any mail to "[EMAIL PROTECTED]" : : -- [EMAIL PROTECTED] _______________________________________________ freebsd-performance@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "[EMAIL PROTECTED]"
