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[79.179.71.128]) by smtp.gmail.com with ESMTPSA id z127sm6091271wmc.2.2020.10.03.11.43.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 03 Oct 2020 11:43:17 -0700 (PDT) Date: Sat, 3 Oct 2020 14:43:13 -0400 From: "Michael S. Tsirkin" To: David Miller Cc: anant.thazhemadam@gmail.com, jasowang@redhat.com, kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, linux-kernel-mentees@lists.linuxfoundation.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [Linux-kernel-mentees][PATCH 0/2] reorder members of structures in virtio_net for optimization Message-ID: <20201003144300-mutt-send-email-mst@kernel.org> References: <20200930051722.389587-1-anant.thazhemadam@gmail.com> <20201002.190638.1090456279017490485.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201002.190638.1090456279017490485.davem@davemloft.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 02, 2020 at 07:06:38PM -0700, David Miller wrote: > From: Anant Thazhemadam > Date: Wed, 30 Sep 2020 10:47:20 +0530 > > > The structures virtnet_info and receive_queue have byte holes in > > middle, and their members could do with some rearranging > > (order-of-declaration wise) in order to overcome this. > > > > Rearranging the members helps in: > > * elimination the byte holes in the middle of the structures > > * reduce the size of the structure (virtnet_info) > > * have more members stored in one cache line (as opposed to > > unnecessarily crossing the cacheline boundary and spanning > > different cachelines) > > > > The analysis was performed using pahole. > > > > These patches may be applied in any order. > > What effects do these changes have on performance? > > The cache locality for various TX and RX paths could be effected. > > I'm not applying these patches without some data on the performance > impact. > > Thank you. Agree wholeheartedly. -- MST