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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id s5sm10342396qke.120.2020.08.31.10.59.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Aug 2020 10:59:32 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kCo5b-0032Xa-Um; Mon, 31 Aug 2020 14:59:31 -0300 Date: Mon, 31 Aug 2020 14:59:31 -0300 From: Jason Gunthorpe To: doug@easyco.com Cc: Sagi Grimberg , linux-rdma@vger.kernel.org, Max Gurtovoy , Stephen Rust , ming Lei Subject: Re: [PATCH] IB/isert: fix unaligned immediate-data handling Message-ID: <20200831175931.GC24045@ziepe.ca> References: <20200830103209.378141-1-sagi@grimberg.me> <20200831121818.GZ24045@ziepe.ca> <8bc2755b-e7d6-5d9c-f5e0-e8036b28beb6@grimberg.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Mon, Aug 31, 2020 at 10:02:15AM -0700, Doug Dumitru wrote: > On Mon, Aug 31, 2020 at 9:48 AM Sagi Grimberg wrote: > > > > > > >> Currently we allocate rx buffers in a single contiguous buffers > > >> for headers (iser and iscsi) and data trailer. This means > > >> that most likely the data starting offset is aligned to 76 > > >> bytes (size of both headers). > > >> > > >> This worked fine for years, but at some point this broke. > > >> To fix this, we should avoid passing unaligned buffers for > > >> I/O. > > > > > > That is a bit vauge - what suddenly broke it? > > > > Somewhere around the multipage bvec work that Ming did. The issue was > > that brd assumed a 512 aligned page vector. IIRC the discussion settled > > that the block layer expects a 512B aligned buffer(s). > > I will second that block layers expect "at least" 512B aligned > buffers. Many of them get less efficient when bvecs are not full, 4K > aligned, pages. Can we put all this info in the commit message please? Thanks, Jason