From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Abeni Subject: Re: [PATCH] IB/ipoib: move back the IB LL address into the hard header Date: Tue, 11 Oct 2016 20:10:07 +0200 Message-ID: <1476209407.448.9.camel@redhat.com> References: <1dbd83dfe7f435eecc5bc460e901b47758280f30.1476206016.git.pabeni@redhat.com> <20161011173216.GA16892@obsidianresearch.com> <22f61258-9bcf-0adc-f23f-79a4f1d50c6a@redhat.com> <20161011180119.GB17319@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Doug Ledford , linux-rdma@vger.kernel.org, Sean Hefty , Hal Rosenstock , netdev@vger.kernel.org To: Jason Gunthorpe Return-path: Received: from mx1.redhat.com ([209.132.183.28]:45972 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753244AbcJKSKM (ORCPT ); Tue, 11 Oct 2016 14:10:12 -0400 In-Reply-To: <20161011180119.GB17319@obsidianresearch.com> Sender: netdev-owner@vger.kernel.org List-ID: 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.