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[80.230.31.118]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324ea82f6asm42036674f8f.27.2025.12.25.08.27.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Dec 2025 08:27:46 -0800 (PST) Date: Thu, 25 Dec 2025 11:27:43 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: Xuan Zhuo , netdev@vger.kernel.org, Eugenio =?iso-8859-1?Q?P=E9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Bui Quang Minh Subject: Re: [PATCH net 1/3] virtio-net: make refill work a per receive queue work Message-ID: <20251225112729-mutt-send-email-mst@kernel.org> References: <20251223152533.24364-1-minhquangbui99@gmail.com> <20251223152533.24364-2-minhquangbui99@gmail.com> <1766540234.3618076-1-xuanzhuo@linux.alibaba.com> <20251223204555-mutt-send-email-mst@kernel.org> 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 Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Dec 25, 2025 at 03:33:29PM +0800, Jason Wang wrote: > On Wed, Dec 24, 2025 at 9:48 AM Michael S. Tsirkin wrote: > > > > On Wed, Dec 24, 2025 at 09:37:14AM +0800, Xuan Zhuo wrote: > > > > > > Hi Jason, > > > > > > I'm wondering why we even need this refill work. Why not simply let NAPI retry > > > the refill on its next run if the refill fails? That would seem much simpler. > > > This refill work complicates maintenance and often introduces a lot of > > > concurrency issues and races. > > > > > > Thanks. > > > > refill work can refill from GFP_KERNEL, napi only from ATOMIC. > > > > And if GFP_ATOMIC failed, aggressively retrying might not be a great idea. > > Btw, I see some drivers are doing things as Xuan said. E.g > mlx5e_napi_poll() did: > > busy |= INDIRECT_CALL_2(rq->post_wqes, > mlx5e_post_rx_mpwqes, > mlx5e_post_rx_wqes, > > ... > > if (busy) { > if (likely(mlx5e_channel_no_affinity_change(c))) { > work_done = budget; > goto out; > ... is busy a GFP_ATOMIC allocation failure? > > > > Not saying refill work is a great hack, but that is the reason for it. > > -- > > MST > > > > Thanks