MBUF statistics

Bosko Milekic bosko.milekic at gmail.com
Tue Feb 15 14:27:57 PST 2005

On Tue, 15 Feb 2005 16:54:52 +0100, Max Laier <max at love2party.net> wrote:
> On Tuesday 15 February 2005 12:38, Borja Marcos wrote:
> >       Hello,
> >
> >       Looking at the mbuf statistics available in FreeBSD 4 and FreeBSD 5 I
> > can see that the statistics available in FreeBSD 5 are, surprisingly,
> > much less comprehensive. Is there any other place where I can find out
> > how many mbuf requests have been done, how many of them have waited,
> > how many have failed, etc?
> I use "$vmstat -z | grep Mbuf".  The netstat -m output is broken, because
> fixing this would impose an additional atomic operation on each alloc/free
> which is a real performance killer.

Yeah, unfortunately statistics are too hard to do completely correctly
right now (too hard on performance, that is).  To make things worse,
the more involved UMA zone design used for Mbuf and Cluster
allocations means that some of the UMA zone statistics you get with
"vmstat -z" are not entirely accurate.  The UMA zone statistics code
needs to be changed to accomodate this structure, but in addition to
that a way to make statistics gathering cheaper would be nice, because
currently doing a 'vmstat -z' is really terrible for performance. 
Which reminds me... those of you doing benchmarks, please don't run
'vmstat -z' while you're doing them, it might skew/pessimize your

Bosko Milekic - If I were a number, I'd be irrational.
Contact Info: http://bmilekic.unixdaemons.com/contact.txt

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