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[146.241.231.196]) by smtp.gmail.com with ESMTPSA id r15-20020adfe68f000000b003111025ec67sm15279253wrm.25.2023.06.29.01.42.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jun 2023 01:42:36 -0700 (PDT) Message-ID: <36c95dd6babb2202f70594d5dde13493af62dcad.camel@redhat.com> Subject: Re: [Patch v3] net: mana: Batch ringing RX queue doorbell on receiving packets From: Paolo Abeni To: longli@linuxonhyperv.com, Jason Gunthorpe , Leon Romanovsky , Ajay Sharma , Dexuan Cui , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , "David S. Miller" , Eric Dumazet , Jakub Kicinski Cc: linux-rdma@vger.kernel.org, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Long Li , stable@vger.kernel.org Date: Thu, 29 Jun 2023 10:42:34 +0200 In-Reply-To: <1687823827-15850-1-git-send-email-longli@linuxonhyperv.com> References: <1687823827-15850-1-git-send-email-longli@linuxonhyperv.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Mon, 2023-06-26 at 16:57 -0700, longli@linuxonhyperv.com wrote: > From: Long Li >=20 > It's inefficient to ring the doorbell page every time a WQE is posted to > the received queue. Excessive MMIO writes result in CPU spending more > time waiting on LOCK instructions (atomic operations), resulting in > poor scaling performance. >=20 > Move the code for ringing doorbell page to where after we have posted all > WQEs to the receive queue during a callback from napi_poll(). >=20 > With this change, tests showed an improvement from 120G/s to 160G/s on a > 200G physical link, with 16 or 32 hardware queues. >=20 > Tests showed no regression in network latency benchmarks on single > connection. >=20 > While we are making changes in this code path, change the code for > ringing doorbell to set the WQE_COUNT to 0 for Receive Queue. The > hardware specification specifies that it should set to 0. Although > currently the hardware doesn't enforce the check, in the future releases > it may do. >=20 > Cc: stable@vger.kernel.org > Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure Network= Adapter (MANA)") Uhmmm... this looks like a performance improvement to me, more suitable for the net-next tree ?!? (Note that net-next is closed now). In any case you must avoid empty lines in the tag area. If you really intend targeting the -net tree, please repost fixing the above and explicitly specifying the target tree in the subj prefix. thanks! Paolo