On Wed, 2006-09-13 at 15:13, Michael S. Tsirkin wrote: > Quoting r. Hal Rosenstock <[EMAIL PROTECTED]>: > > Subject: Re: [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K > > > > On Wed, 2006-09-13 at 12:22, Michael S. Tsirkin wrote: > > > Quoting r. Hal Rosenstock <[EMAIL PROTECTED]>: > > > > Subject: Re: [openib-general] [PATCH for-2.6.18] IB/cma: option to > > > > limitMTU to 1K > > > > > > > > On Wed, 2006-09-13 at 11:57, Michael S. Tsirkin wrote: > > > > > Tavor systems get better performance with 1K MTU. Since there does > > > > > not seem to be any way to find out whether the remote system uses > > > > > Tavor, > > > > > add an option to limit the MTU globally. > > > > > > > > Can't Tavor be determined locally ? > > > > > > It can, but we need this for remote tavor as well, anyway. > > > > > > > And couldn't the remote end negotiate the MTU down (if Tavor) as well ? > > > > > > The way to do this is would be for SA to select 1K MTU if it detects > > > Tavor on one side > > > and if this does not conflict with MTU selector. > > > > But it only needs the MTU on each local side (once for the REQ and on > > the remote side for the REP). It would mean that if the local side were > > capable of larger MTU and the remote side were Tavor, that the REQ would > > be REJ with MTU too large and need to be retried at a smaller MTU. > > This has 3 implications that make it impractical: > . connection rate will suffer greatly > . this will need ot be done in each ulp, and it's a lot of code > . protocols such as sdp explicitly say what to do on rej > and do not seem to speak about retries
OK. > > > However > > > 1. Even opensm does not implement this optimization yet > > > > What optimization ? I don't understand what you are saying OpenSM > > doesn't support. > > > > > 2. We need to work with existing SMs too > > > > Not sure what the SA issue is here. > > If path MTU selector in path query allows MTU 1K (e.g. "best MTU") > and one of the sides is Tavor, select the best MTU that is 1K > and not the largest possible. How would it be identified if the SA supports this ? > If path MTU selector requires 2K MTU, return path with 2K MTU. Also, I'm not sure that this is the required difference in the SA requests :-( -- Hal _______________________________________________ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
