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([2a0d:3344:2712:7e10:4d59:d956:544f:d65c]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e82aa29328sm1151256185a.33.2025.08.14.02.39.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Aug 2025 02:39:43 -0700 (PDT) Message-ID: <0277b2b5-b3f4-41da-8c18-e6131f908fd3@redhat.com> Date: Thu, 14 Aug 2025 11:39:41 +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 v4 1/4] net: ethtool: support including Flow Label in the flow hash for RSS To: Jakub Kicinski , davem@davemloft.net Cc: netdev@vger.kernel.org, edumazet@google.com, andrew+netdev@lunn.ch, horms@kernel.org, donald.hunter@gmail.com, michael.chan@broadcom.com, pavan.chebbi@broadcom.com, willemdebruijn.kernel@gmail.com, ecree.xilinx@gmail.com, andrew@lunn.ch References: <20250811234212.580748-1-kuba@kernel.org> <20250811234212.580748-2-kuba@kernel.org> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20250811234212.580748-2-kuba@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/12/25 1:42 AM, Jakub Kicinski wrote: > It is expected that the hash communicated to the host > may change if the Flow Label changes. This may be surprising > to some host software, but I don't expect the devices > can compute two Toeplitz hashes, one with the Flow Label > for queue selection and one without for the rx hash > communicated to the host. Besides, changing the hash > may potentially help to change the path thru host queues. > User can disable NETIF_F_RXHASH if they require a stable > flow hash. FWIW, my understanding is that the S/W computed RX hash includes by default the flow label, as skb_get_hash()/__skb_get_hash_net() dissect with FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL and the latter force the flowlabel inclusion when available. AFAICS enabling RXH_IP6_FL will make the H/W and S/W hashing consistent. /P