svn commit: r242029 - head/sys/kern

[John Baldwin]

On Thursday, October 25, 2012 4:05:51 am Konstantin Belousov wrote:
> On Thu, Oct 25, 2012 at 01:46:21AM +0000, Alfred Perlstein wrote:
> > Author: alfred
> > Date: Thu Oct 25 01:46:20 2012
> > New Revision: 242029
> > URL: http://svn.freebsd.org/changeset/base/242029
> > 
> > Log:
> >   Allow autotune maxusers > 384 on 64 bit machines
> >   
> >   A default install on large memory machines with multiple 10gigE interfaces
> >   were not being given enough mbufs to do full bandwidth TCP or NFS traffic.
> >   
> >   To keep the value somewhat reasonable, we scale back the number of
> >   maxuers by 1/6 past the 384 point.  This gives us enough mbufs for most
> >   of our pretty basic 10gigE line-speed tests to complete.
> > 
> > Modified:
> >   head/sys/kern/subr_param.c
> > 
> > Modified: head/sys/kern/subr_param.c
> > ==============================================================================
> > --- head/sys/kern/subr_param.c	Thu Oct 25 01:27:01 2012	(r242028)
> > +++ head/sys/kern/subr_param.c	Thu Oct 25 01:46:20 2012	(r242029)
> > @@ -278,8 +278,16 @@ init_param2(long physpages)
> >  		maxusers = physpages / (2 * 1024 * 1024 / PAGE_SIZE);
> >  		if (maxusers < 32)
> >  			maxusers = 32;
> > -		if (maxusers > 384)
> > -			maxusers = 384;
> > +		/*
> > +		 * Clips maxusers to 384 on machines with <= 4GB RAM or 32bit.
> > +		 * Scales it down 6x for large memory machines.
> > +		 */
> > +		if (maxusers > 384) {
> > +			if (sizeof(void *) <= 4)
> > +			    maxusers = 384;
> > +			else
> > +			    maxusers = 384 + ((maxusers - 384) / 6);
> > +		}
> This is unbelievably weird way to express the '64bit'. The
> #ifdef _LP64 is enough there instead of the runtime check.
> 
> Also, are you sure that all our 64bit arches do not have KVA limitations ?

There is an active thread on current@ with a different patch that uses a KVA
constant to derive 384 instead.  When we have updated tuning in the past
(e.g. adjusting the cap on maxvnodes), there was a bit of discussion rather
than a random drive by commit.  I think we should probably hold off on making
changes here and figure out what the right way to fix this is in the thread on
current@ instead.  Andre has already suggested divorcing mbuf tuning from
maxusers entirely for example.

-- 
John Baldwin