[openib-general] [PATCH] osm: PathRecord prefer 1K MTU for MT23108 devices

[Rimmer, Todd]

> From: Eitan Zahavi [mailto:eitan at mellanox.co.il]
> Sent: Monday, September 18, 2006 4:17 PM
> To: Rimmer, Todd
> Cc: Michael S. Tsirkin; Or Gerlitz; OPENIB
> Subject: Re: [openib-general] [PATCH] osm: PathRecord prefer 1K MTU
for
> MT23108 devices
> 

> >The patch you submitted only modified Open SM.  So please show me the
> >patch where MVAPICH, Open MPI, SDP, SRP and other ULPs allow this to
be
> >tuned by the user or application?  Lacking that patch, all the "if a
ULP
> >wants" statements above are mute.  The goal is for OFED to provide a
> >high performance standard solution.  If end users must modify the
ULPs
> >source code to achieve that goal, OFED misses the mark.
> >
> >
> To our best knowledge the change which automatically selects 1K MTU
for
> the above ULPs improves their performance.
> Do you have any measurement on OFED 1.1 that shows otherwise? Under
what
> cases?
> If this is the case then you basically do not have to do anything and
> all just works as it used to.
> But if we are correct then a user can create an OpenSM cache file,
> modify the enable_quirks to TRUE and restart the SM.
> I am sure you could imaging this patch was not just another way for us
> to spend our time...
> 

In my previous posting I included MPI performance numbers which showed
>1K <2K performance was reduced when using 2K MTU.  This also applies to
SDP when an existing application is using message sizes in this range
(which is quite common).

Having control only in the SM is not sufficient.  Having to bounce the
SM is even worse.

Todd Rimmer