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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Kuniyuki Iwashima , Willem de Bruijn , Neal Cardwell , David Ahern , Arnd Bergmann , Jonathan Corbet , Andrew Lunn , Shuah Khan , Donald Hunter , Mina Almasry Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Stanislav Fomichev , Bobby Eshleman Subject: Re: [PATCH net-next v7 0/5] net: devmem: improve cpu cost of RX token management Message-ID: References: <20251119-scratch-bobbyeshleman-devmem-tcp-token-upstream-v7-0-1abc8467354c@meta.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251119-scratch-bobbyeshleman-devmem-tcp-token-upstream-v7-0-1abc8467354c@meta.com> On Wed, Nov 19, 2025 at 07:37:07PM -0800, Bobby Eshleman wrote: > This series improves the CPU cost of RX token management by adding an > attribute to NETDEV_CMD_BIND_RX that configures sockets using the > binding to avoid the xarray allocator and instead use a per-binding niov > array and a uref field in niov. > > Improvement is ~13% cpu util per RX user thread. > > Using kperf, the following results were observed: > > Before: > Average RX worker idle %: 13.13, flows 4, test runs 11 > After: > Average RX worker idle %: 26.32, flows 4, test runs 11 > > Two other approaches were tested, but with no improvement. Namely, 1) > using a hashmap for tokens and 2) keeping an xarray of atomic counters > but using RCU so that the hotpath could be mostly lockless. Neither of > these approaches proved better than the simple array in terms of CPU. > > The attribute NETDEV_A_DMABUF_AUTORELEASE is added to toggle the > optimization. It is an optional attribute and defaults to 0 (i.e., > optimization on). > [...] > > Changes in v7: > - use netlink instead of sockopt (Stan) > - restrict system to only one mode, dmabuf bindings can not co-exist > with different modes (Stan) > - use static branching to enforce single system-wide mode (Stan) > - Link to v6: https://lore.kernel.org/r/20251104-scratch-bobbyeshleman-devmem-tcp-token-upstream-v6-0-ea98cf4d40b3@meta.com > Mina, I was wondering if you had any feedback on this approach? Best, Bobby