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Hermes SMTP Server) with ESMTPA ID 659144cf4e3f782bde76ce13dad45cc9; Mon, 06 Apr 2026 07:58:31 +0000 (UTC) Message-ID: Date: Mon, 6 Apr 2026 09:58:24 +0200 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 v8 00/11] net: tunnel: introduce noref xmit flows for tunnels Content-Language: en-US To: Paolo Abeni , netdev@vger.kernel.org, sd@queasysnail.net, kuba@kernel.org Cc: Jason@zx2c4.com References: <20260312155657.25676-1-mmietus97.ref@yahoo.com> <20260312155657.25676-1-mmietus97@yahoo.com> <726e1d40-6a29-4e6f-964c-1a4d0cf7d4eb@redhat.com> From: Marek Mietus In-Reply-To: <726e1d40-6a29-4e6f-964c-1a4d0cf7d4eb@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Mailer: WebService/1.1.25495 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.yahoo W dniu 17.03.2026 o 12:37, Paolo Abeni pisze: > On 3/12/26 4:56 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: 72.52 gb/sec, stddev = 1.39 >> patched: 75.39 gb/sec, stddev = 0.94 >> >> 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. > > Sabrina noted I wrongly replied on an old revision. Reporting my > statements here for completeness. > > 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. > > Side note: if you are interested into improving (UDP) tunnel > performances have a look to big TCP support work from Alice Mikityanska: > > https://lore.kernel.org/netdev/20260226201600.222044-1-alice.kernel@fastmail.im/ > > /P > > Hi Paolo, Could you clarify what would be a more realistic test setup? I'm assuming using physical interfaces would yield more realistic results. Also, what performance benefit would be worth this kind of "code churn"? What kind of margins were you looking for? I got mixed signals from you and Sabrina, so these clarifications would go a long way. P.S - I'll take a closer look at Alice Mikityanska's "big TCP" works.