On Tue, 2016-10-11 at 12:01 -0600, Jason Gunthorpe wrote: > > AFAICS the max mtu is already underlying h/w dependent, how does such > > differences are currently coped by ? (I'm sorry I lack some/a lot of IB > > back-ground) > > It isn't h/w dependent. In CM mode the MTU is 65520 because that is > what is hard coded into the ipoib driver. We tell everyone to use that > number. Eg see RH's docs on the subject: > > https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/sec-Configuring_IPoIB.html > > AFAIK, today everyone just wires that number into their scripts, so we > have to mass change everything to the smaller number. That sounds > really hard, IMHO if there is any way to avoid it we should, even if > it is a little costly.
Thank you for the details! The first s/g fragment (the head buffer) is not allocated with the page allocator, so perhaps there is some not too difficult/costly way out of this.
