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Tue, 17 Mar 2026 04:02:31 -0700 (PDT) Received: from [192.168.88.32] ([216.128.11.95]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b9791c113d4sm624943566b.6.2026.03.17.04.02.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Mar 2026 04:02:31 -0700 (PDT) Message-ID: <89df6470-027b-4d86-98a1-72042ca819ed@redhat.com> Date: Tue, 17 Mar 2026 12:02:30 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v5 00/11] net: tunnel: introduce noref xmit flows for tunnels To: Marek Mietus , netdev@vger.kernel.org, sd@queasysnail.net, kuba@kernel.org Cc: Jason@zx2c4.com References: <20260113162954.5948-1-mmietus97.ref@yahoo.com> <20260113162954.5948-1-mmietus97@yahoo.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260113162954.5948-1-mmietus97@yahoo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/13/26 5:29 PM, Marek Mietus wrote: > Currently, tunnel xmit flows always take a reference on the dst_entry > for each xmitted packet. These atomic operations are redundant in some > flows. > > This patchset introduces the infrastructure required for converting > the tunnel xmit flows to noref, and converts them where possible. > > These changes improve tunnel performance, since less atomic operations > are used. > > There are already noref optimizations in both ipv4 and ip6. > (See __ip_queue_xmit, inet6_csk_xmit) > This patchset implements similar optimizations in ip and udp tunnels. > > Benchmarks: > I used a vxlan tunnel over a pair of veth peers and measured the average > throughput over multiple samples. > > I ran 100 samples on a clean build, and another 100 on a patched > build. Each sample ran for 120 seconds. These were my results: > > clean: 71.95 mb/sec, stddev = 1.71 > patched: 74.92 mb/sec, stddev = 1.35 > > TL;DR - This patchset results in a 4% improvement in throughput for > vxlan. It's safe to assume that we might see similar results when testing > other tunnels. IMHO this performance delta is not enough to justify this amount of changes. Additionally, the measured impact of removing the dst_hold/dst_release does not fit with my direct experience on the same matter: it should be below noise level in practice, as dst are per-cpu and and no contention/false sharing is expected in a good setup. I think you are observing larger impact because in the veth test dst_release can happen on a remote CPU. Note that this setup (vxlan over veth) is not very relevant in practice. I'm sorry I'm not applying this series. /P