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[80.230.31.118]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d19352306sm344339415e9.5.2025.12.25.08.27.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Dec 2025 08:27:12 -0800 (PST) Date: Thu, 25 Dec 2025 11:27:09 -0500 From: "Michael S. Tsirkin" To: Bui Quang Minh Cc: Xuan Zhuo , Jason Wang , 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 Subject: Re: [PATCH net 1/3] virtio-net: make refill work a per receive queue work Message-ID: <20251225112636-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> <75e32d60-51b1-4c46-bd43-d17af7440e74@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Dec 25, 2025 at 10:55:36PM +0700, Bui Quang Minh wrote: > On 12/24/25 23:49, Bui Quang Minh wrote: > > On 12/24/25 08:47, 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. > > > > > > Not saying refill work is a great hack, but that is the reason for it. > > > > In case no allocated received buffer and NAPI refill fails, the host > > will not send any packets. If there is no busy polling loop either, the > > RX will be stuck. That's also the reason why we need refill work. Is it > > correct? > > I've just looked at mlx5e_napi_poll which is mentioned by Jason. So if we > want to retry refilling in the next NAPI, we can set a bool (e.g. > retry_refill) in virtnet_receive, then in virtnet_poll, we don't call > virtqueue_napi_complete. As a result, our napi poll is still in the > softirq's poll list, so we don't need a new host packet to trigger > virtqueue's callback which calls napi_schedule again. > > > > Thanks, > > Quang Minh. > > > yes yes. but aggressively retrying GFP_ATOMIC until it works is not the thing to do. -- MST