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([2001:ee0:4f4c:210:77e8:13fb:83fb:4ed6]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a2f3c839b7sm185337805ad.37.2025.12.25.07.55.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Dec 2025 07:55:42 -0800 (PST) Message-ID: Date: Thu, 25 Dec 2025 22:55:36 +0700 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 1/3] virtio-net: make refill work a per receive queue work From: Bui Quang Minh To: "Michael S. Tsirkin" , Xuan Zhuo Cc: Jason Wang , netdev@vger.kernel.org, =?UTF-8?Q?Eugenio_P=C3=A9rez?= , 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 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> Content-Language: en-US In-Reply-To: <75e32d60-51b1-4c46-bd43-d17af7440e74@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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. > >