Re: [BProc] page allocation problems

[Dale H. <ro...@ma...>]

On Mon, May 09, 2005 at 10:54:16AM -0700, Erik Hendriks elucidated:
> On 5/7/05, Dale Harris <ro...@ma...> wrote:
> > 
> > Hey I'm seeing some page allocation errors.  Has anyone seen anything
> > like this.  Of course it a 2.6.9 vanilla kernel patched for bproc, and
> > myrinet GM driver is running.
> 
> I don't think this has anything to do with BProc per se.  I've seen
> stuff like this before whenever I turn on jumbo frames on any machine
> and start shoving a lot of data through.  I'm not 100% sure I'm right
> about what's going on but here's my guess:
> 
> Once you start using jumbo frame sizes (~9k) it gets harder to
> allocate skuffs in the kernel.  These are the buffers that hold
> network packets.  Pages for this kind of stuff are allocated in powers
> of two.  9k will require 4 pages.  Also, since it's kernel space stuff


Okay, so this does make sense.  Myrinet is using Jumbo frames and set
itself to a default of MTU of 9000.  Myrinet suggested dropping the
frame size down to 4000.  


With bproc is can I just put a:

plugin ifconfig myri0 mtu 4000


To set the MTU when the nodes boot?  Or does it support setting the MTU?


Dale