Date: Wed, 24 Jul 2002 12:40:43 -0700 From: "Balaji, Pavan" <pavan.balaji@intel.com> To: "'Jeff Jirsa'" <jeff@boris.st.hmc.edu>, "Balaji, Pavan" <pavan.balaji@intel.com> Cc: "'James Snow'" <snow@teardrop.org>, ntai@mac.com, freebsd-questions@FreeBSD.ORG Subject: RE: Number of mbuf clusters (NMBCLUSTERS) Message-ID: <3D386AED1B47D411A94300508B11F18703BC5C27@fmsmsx116.fm.intel.com>
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Oops. Sorry. I didn't know that we had an option to do this in the conf
file. I couldn't find it there though.
Pavan Balaji,
Intel Corporation
"Only the Paranoid Survive" -- Andy Grove
> -----Original Message-----
> From: Jeff Jirsa [mailto:jeff@boris.st.hmc.edu]
> Sent: Wednesday, July 24, 2002 2:32 PM
> To: Balaji, Pavan
> Cc: 'James Snow'; ntai@mac.com; freebsd-questions@FreeBSD.ORG
> Subject: RE: Number of mbuf clusters (NMBCLUSTERS)
>
>
> On Wed, 24 Jul 2002, Balaji, Pavan wrote:
>
> >
> > You can increase the maximum number of clusters in
> /usr/src/sys/sys/sysctl.h
> > and recompile the kernel. But make sure that you have a
> stable kernel image
> > ready, just in case you increase this value so much that
> your kernel doesn't
> > boot ;)
> >
> > I guess the default value is around 9, while for 256MB mem,
> you can go upto
> > maybe 10000 clusters.
>
> That's questionable advice. Reading the tuning(7) man page:
>
>
> NMBCLUSTERS may be adjusted to increase the number of
> network mbufs the
> system is willing to allocate. Each cluster represents
> approximately 2K
> of memory, so a value of 1024 represents 2M of kernel
> memory reserved for
> network buffers. You can do a simple calculation to
> figure out how many
> you need. If you have a web server which maxes out at
> 1000 simultaneous
> connections, and each connection eats a 16K receive and
> 16K send buffer,
> you need approximate 32MB worth of network buffers to
> deal with it. A
> good rule of thumb is to multiply by 2, so 32MBx2 =
> 64MB/2K = 32768. So
> for this case you would want to se NMBCLUSTERS to 32768.
> We recommend
> values between 1024 and 4096 for machines with moderates
> amount of mem-
> ory, and between 4096 and 32768 for machines with greater
> amounts of mem-
> ory. Under no circumstances should you specify an
> arbitrarily high value
> for this parameter, it could lead to a boot-time crash.
> The -m option to
> netstat(1) may be used to observe network cluster use.
>
> Figure out how many connections you'll deal with, and then
> increase the
> value accordingly, rather than simply guessing and possibly wasting
> memory you may want to use elsewhere. I'd also recommend
> modifying your
> kernel config file rather than sysctl.h, and then rebuilding.
>
> - Jeff
>
>
>
>
>
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