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Tue, 17 Mar 2026 07:28:13 -0400 (EDT) Date: Tue, 17 Mar 2026 12:28:10 +0100 From: Sabrina Dubroca To: Paolo Abeni Cc: Marek Mietus , netdev@vger.kernel.org, kuba@kernel.org, Jason@zx2c4.com Subject: Re: [PATCH net-next v5 00/11] net: tunnel: introduce noref xmit flows for tunnels Message-ID: References: <20260113162954.5948-1-mmietus97.ref@yahoo.com> <20260113162954.5948-1-mmietus97@yahoo.com> <89df6470-027b-4d86-98a1-72042ca819ed@redhat.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <89df6470-027b-4d86-98a1-72042ca819ed@redhat.com> 2026-03-17, 12:02:30 +0100, Paolo Abeni wrote: > 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. This is probably fine for everybody who's been following this series, but you answered v5 (from January) instead of v8 (posted last week). -- Sabrina