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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id y194sm1420543qkb.111.2019.07.10.10.25.05 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 10 Jul 2019 10:25:06 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hlGL3-00046r-EV; Wed, 10 Jul 2019 14:25:05 -0300 Date: Wed, 10 Jul 2019 14:25:05 -0300 From: Jason Gunthorpe To: Sagi Grimberg Cc: Danil Kipnis , Jack Wang , linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, axboe@kernel.dk, Christoph Hellwig , bvanassche@acm.org, dledford@redhat.com, Roman Pen , gregkh@linuxfoundation.org Subject: Re: [PATCH v4 00/25] InfiniBand Transport (IBTRS) and Network Block Device (IBNBD) Message-ID: <20190710172505.GD4051@ziepe.ca> References: <20190620150337.7847-1-jinpuwang@gmail.com> <20190710135519.GA4051@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org Archived-At: List-Archive: List-Post: On Wed, Jul 10, 2019 at 09:25:05AM -0700, Sagi Grimberg wrote: > > > > Another question, from what I understand from the code, the client > > > always rdma_writes data on writes (with imm) from a remote pool of > > > server buffers dedicated to it. Essentially all writes are immediate (no > > > rdma reads ever). How is that different than using send wrs to a set of > > > pre-posted recv buffers (like all others are doing)? Is it faster? > > > > RDMA WRITE only is generally a bit faster, and if you use a buffer > > pool in a smart way it is possible to get very good data packing. > > There is no packing, its used exactly as send/recv, but with a remote > buffer pool (pool of 512K buffers) and the client selects one and rdma > write with imm to it. Well that makes little sense then:) > > Maybe this is fine, but it needs to be made very clear that it uses > > this insecure operating model to get higher performance.. > > I still do not understand why this should give any notice-able > performance advantage. Usually omitting invalidations gives a healthy bump. Also, RDMA WRITE is generally faster than READ at the HW level in various ways. Jason