On Wed, 2006-09-13 at 17:49, 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 17:09, 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 15:05, Michael S. Tsirkin wrote: > > > > > Quoting r. Hal Rosenstock <[EMAIL PROTECTED]>: > > > > > > > If I understood Michael's comment properly, this will have the > > > > > > > side > > > > > > > effect that IPoIB won't work since IPoIB requires 2K MTUs. As > > > > > > > far as > > > > > > > I know, there is no way to specify whether a path is needed for > > > > > > > UD vs. > > > > > > > RC in the path query. > > > > > > > > > > > > I don't know how either. I don't think it can be done (at least > > > > > > currently per the standard). > > > > > > > > > > We don't really need to know whether path is for RC or UD QP. > > > > > IPoIB needs MTU >= 2K so it should set mtu selector to >= 2K. > > > > > > > > That's the default and not the minimum MTU (for IPoIB). > > > > > > How isn't it? > > > > Look at RFC 4391 as to the requirement. > > I'm talking about our implementation not the spec.
Don't we risk interop issues by relying on things not required in the spec ? > > > By default, IPoIB reports 2K MTU to linux. > > > So it will get 2K packets, and since IB swiches > > > can not fragment packets, they will simply get dropped. > > > > With ifconfig, the MTU can be changed. Fragmentation is at the IP layer > > in the end station stack, not the IB switches. > > AFAIK linux won't fragment packets that do not exceed MTU and MSS. > > > > I conclude that IPoIB by default requires minimum mtu of 2K. > > > Right? > > > > Not minimum. > > > > > And it's not a problem since all HCAs support 2K. > > > > or more but it could be less per the RFC. > > Again, if IPoIB implementation does not need 2K mtu there's > no problem to give it 1K in path. If it wants 2K MTU it must > set selector accordingly. _______________________________________________ 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
