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Fri, 28 Nov 2025 06:20:12 -0800 (PST) X-Google-Smtp-Source: AGHT+IFPEkA/LoZdallg49g1MUTRCeyrnm9WywP2P1KOTjKBH4y40uAcYN4UEnTmkp4kPiOrnajn8Q== X-Received: by 2002:a05:6000:1a8f:b0:42b:3c25:cd06 with SMTP id ffacd0b85a97d-42cc1cee419mr30438877f8f.22.1764339612057; Fri, 28 Nov 2025 06:20:12 -0800 (PST) Received: from [192.168.88.32] ([212.105.155.212]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42e1c5c304csm9948281f8f.8.2025.11.28.06.20.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Nov 2025 06:20:11 -0800 (PST) Message-ID: <8fa70565-0f4a-4a73-a464-5530b2e29fa5@redhat.com> Date: Fri, 28 Nov 2025 15:20:09 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v3 2/3] xsk: use atomic operations around cached_prod for copy mode To: Jason Xing , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, horms@kernel.org, andrew+netdev@lunn.ch Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing References: <20251128134601.54678-1-kerneljasonxing@gmail.com> <20251128134601.54678-3-kerneljasonxing@gmail.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20251128134601.54678-3-kerneljasonxing@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/28/25 2:46 PM, Jason Xing wrote: > From: Jason Xing > > Use atomic_try_cmpxchg operations to replace spin lock. Technically > CAS (Compare And Swap) is better than a coarse way like spin-lock > especially when we only need to perform a few simple operations. > Similar idea can also be found in the recent commit 100dfa74cad9 > ("net: dev_queue_xmit() llist adoption") that implements the lockless > logic with the help of try_cmpxchg. > > Signed-off-by: Jason Xing > --- > Paolo, sorry that I didn't try to move the lock to struct xsk_queue > because after investigation I reckon try_cmpxchg can add less overhead > when multiple xsks contend at this point. So I hope this approach > can be adopted. I still think that moving the lock would be preferable, because it makes sense also from a maintenance perspective. Can you report the difference you measure atomics vs moving the spin lock? Have you tried moving cq_prod_lock, too? /P