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[178.94.201.59]) by smtp.gmail.com with ESMTPSA id o11sm799392lfl.15.2019.07.04.02.53.07 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 04 Jul 2019 02:53:08 -0700 (PDT) Date: Thu, 4 Jul 2019 12:53:06 +0300 From: Ivan Khoronzhuk To: Ilias Apalodimas Cc: Jesper Dangaard Brouer , grygorii.strashko@ti.com, hawk@kernel.org, davem@davemloft.net, ast@kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, xdp-newbies@vger.kernel.org, netdev@vger.kernel.org, daniel@iogearbox.net, jakub.kicinski@netronome.com, john.fastabend@gmail.com Subject: Re: [PATCH v6 net-next 5/5] net: ethernet: ti: cpsw: add XDP support Message-ID: <20190704095305.GC19839@khorivan> Mail-Followup-To: Ilias Apalodimas , Jesper Dangaard Brouer , grygorii.strashko@ti.com, hawk@kernel.org, davem@davemloft.net, ast@kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, xdp-newbies@vger.kernel.org, netdev@vger.kernel.org, daniel@iogearbox.net, jakub.kicinski@netronome.com, john.fastabend@gmail.com References: <20190703101903.8411-1-ivan.khoronzhuk@linaro.org> <20190703101903.8411-6-ivan.khoronzhuk@linaro.org> <20190704111939.5d845071@carbon> <20190704093902.GA26927@apalos> <20190704094329.GA19839@khorivan> <20190704094938.GA27382@apalos> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20190704094938.GA27382@apalos> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Jul 04, 2019 at 12:49:38PM +0300, Ilias Apalodimas wrote: >On Thu, Jul 04, 2019 at 12:43:30PM +0300, Ivan Khoronzhuk wrote: >> On Thu, Jul 04, 2019 at 12:39:02PM +0300, Ilias Apalodimas wrote: >> >On Thu, Jul 04, 2019 at 11:19:39AM +0200, Jesper Dangaard Brouer wrote: >> >>On Wed, 3 Jul 2019 13:19:03 +0300 >> >>Ivan Khoronzhuk wrote: >> >> >> >>> Add XDP support based on rx page_pool allocator, one frame per page. >> >>> Page pool allocator is used with assumption that only one rx_handler >> >>> is running simultaneously. DMA map/unmap is reused from page pool >> >>> despite there is no need to map whole page. >> >>> >> >>> Due to specific of cpsw, the same TX/RX handler can be used by 2 >> >>> network devices, so special fields in buffer are added to identify >> >>> an interface the frame is destined to. Thus XDP works for both >> >>> interfaces, that allows to test xdp redirect between two interfaces >> >>> easily. Aslo, each rx queue have own page pools, but common for both >> >>> netdevs. >> >>> >> >>> XDP prog is common for all channels till appropriate changes are added >> >>> in XDP infrastructure. Also, once page_pool recycling becomes part of >> >>> skb netstack some simplifications can be added, like removing >> >>> page_pool_release_page() before skb receive. >> >>> >> >>> In order to keep rx_dev while redirect, that can be somehow used in >> >>> future, do flush in rx_handler, that allows to keep rx dev the same >> >>> while reidrect. It allows to conform with tracing rx_dev pointed >> >>> by Jesper. >> >> >> >>So, you simply call xdp_do_flush_map() after each xdp_do_redirect(). >> >>It will kill RX-bulk and performance, but I guess it will work. >> >> >> >>I guess, we can optimized it later, by e.g. in function calling >> >>cpsw_run_xdp() have a variable that detect if net_device changed >> >>(priv->ndev) and then call xdp_do_flush_map() when needed. >> >I tried something similar on the netsec driver on my initial development. >> >On the 1gbit speed NICs i saw no difference between flushing per packet vs >> >flushing on the end of the NAPI handler. >> >The latter is obviously better but since the performance impact is negligible on >> >this particular NIC, i don't think this should be a blocker. >> >Please add a clear comment on this and why you do that on this driver, >> >so people won't go ahead and copy/paste this approach >> Sry, but I did this already, is it not enouph? >The flush *must* happen there to avoid messing the following layers. The comment >says something like 'just to be sure'. It's not something that might break, it's >something that *will* break the code and i don't think that's clear with the >current comment. > >So i'd prefer something like >'We must flush here, per packet, instead of doing it in bulk at the end of >the napi handler.The RX devices on this particular hardware is sharing a >common queue, so the incoming device might change per packet' Sounds good, will replace on it. -- Regards, Ivan Khoronzhuk