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([2a01:e0a:e10:ef90:343a:68f:2e91:95c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca5a5b4sm18733188f8f.21.2025.05.21.01.47.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 01:47:56 -0700 (PDT) Message-ID: Date: Wed, 21 May 2025 10:47:55 +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 2/2] virtio_net: Enforce minimum TX ring size for reliability To: "Michael S. Tsirkin" Cc: Jason Wang , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Xuan Zhuo References: <20250520110526.635507-1-lvivier@redhat.com> <20250520110526.635507-3-lvivier@redhat.com> <4085eec2-6d1c-4769-9b0e-5b5771b3e4bf@redhat.com> <20250521043819-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Laurent Vivier Autocrypt: addr=lvivier@redhat.com; keydata= xsFNBFYFJhkBEAC2me7w2+RizYOKZM+vZCx69GTewOwqzHrrHSG07MUAxJ6AY29/+HYf6EY2 WoeuLWDmXE7A3oJoIsRecD6BXHTb0OYS20lS608anr3B0xn5g0BX7es9Mw+hV/pL+63EOCVm SUVTEQwbGQN62guOKnJJJfphbbv82glIC/Ei4Ky8BwZkUuXd7d5NFJKC9/GDrbWdj75cDNQx UZ9XXbXEKY9MHX83Uy7JFoiFDMOVHn55HnncflUncO0zDzY7CxFeQFwYRbsCXOUL9yBtqLer Ky8/yjBskIlNrp0uQSt9LMoMsdSjYLYhvk1StsNPg74+s4u0Q6z45+l8RAsgLw5OLtTa+ePM JyS7OIGNYxAX6eZk1+91a6tnqfyPcMbduxyBaYXn94HUG162BeuyBkbNoIDkB7pCByed1A7q q9/FbuTDwgVGVLYthYSfTtN0Y60OgNkWCMtFwKxRaXt1WFA5ceqinN/XkgA+vf2Ch72zBkJL RBIhfOPFv5f2Hkkj0MvsUXpOWaOjatiu0fpPo6Hw14UEpywke1zN4NKubApQOlNKZZC4hu6/ 8pv2t4HRi7s0K88jQYBRPObjrN5+owtI51xMaYzvPitHQ2053LmgsOdN9EKOqZeHAYG2SmRW LOxYWKX14YkZI5j/TXfKlTpwSMvXho+efN4kgFvFmP6WT+tPnwARAQABzSNMYXVyZW50IFZp dmllciA8bHZpdmllckByZWRoYXQuY29tPsLBeAQTAQIAIgUCVgVQgAIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQ8ww4vT8vvjwpgg//fSGy0Rs/t8cPFuzoY1cex4limJQfReLr SJXCANg9NOWy/bFK5wunj+h/RCFxIFhZcyXveurkBwYikDPUrBoBRoOJY/BHK0iZo7/WQkur 6H5losVZtrotmKOGnP/lJYZ3H6OWvXzdz8LL5hb3TvGOP68K8Bn8UsIaZJoeiKhaNR0sOJyI YYbgFQPWMHfVwHD/U+/gqRhD7apVysxv5by/pKDln1I5v0cRRH6hd8M8oXgKhF2+rAOL7gvh jEHSSWKUlMjC7YwwjSZmUkL+TQyE18e2XBk85X8Da3FznrLiHZFHQ/NzETYxRjnOzD7/kOVy gKD/o7asyWQVU65mh/ECrtjfhtCBSYmIIVkopoLaVJ/kEbVJQegT2P6NgERC/31kmTF69vn8 uQyW11Hk8tyubicByL3/XVBrq4jZdJW3cePNJbTNaT0d/bjMg5zCWHbMErUib2Nellnbg6bc 2HLDe0NLVPuRZhHUHM9hO/JNnHfvgiRQDh6loNOUnm9Iw2YiVgZNnT4soUehMZ7au8PwSl4I KYE4ulJ8RRiydN7fES3IZWmOPlyskp1QMQBD/w16o+lEtY6HSFEzsK3o0vuBRBVp2WKnssVH qeeV01ZHw0bvWKjxVNOksP98eJfWLfV9l9e7s6TaAeySKRRubtJ+21PRuYAxKsaueBfUE7ZT 7zfOwU0EVgUmGQEQALxSQRbl/QOnmssVDxWhHM5TGxl7oLNJms2zmBpcmlrIsn8nNz0rRyxT 460k2niaTwowSRK8KWVDeAW6ZAaWiYjLlTunoKwvF8vP3JyWpBz0diTxL5o+xpvy/Q6YU3BN efdq8Vy3rFsxgW7mMSrI/CxJ667y8ot5DVugeS2NyHfmZlPGE0Nsy7hlebS4liisXOrN3jFz asKyUws3VXek4V65lHwB23BVzsnFMn/bw/rPliqXGcwl8CoJu8dSyrCcd1Ibs0/Inq9S9+t0 VmWiQWfQkz4rvEeTQkp/VfgZ6z98JRW7S6l6eophoWs0/ZyRfOm+QVSqRfFZdxdP2PlGeIFM C3fXJgygXJkFPyWkVElr76JTbtSHsGWbt6xUlYHKXWo+xf9WgtLeby3cfSkEchACrxDrQpj+ Jt/JFP+q997dybkyZ5IoHWuPkn7uZGBrKIHmBunTco1+cKSuRiSCYpBIXZMHCzPgVDjk4viP brV9NwRkmaOxVvye0vctJeWvJ6KA7NoAURplIGCqkCRwg0MmLrfoZnK/gRqVJ/f6adhU1oo6 z4p2/z3PemA0C0ANatgHgBb90cd16AUxpdEQmOCmdNnNJF/3Zt3inzF+NFzHoM5Vwq6rc1JP jfC3oqRLJzqAEHBDjQFlqNR3IFCIAo4SYQRBdAHBCzkM4rWyRhuVABEBAAHCwV8EGAECAAkF AlYFJhkCGwwACgkQ8ww4vT8vvjwg9w//VQrcnVg3TsjEybxDEUBm8dBmnKqcnTBFmxN5FFtI WlEuY8+YMiWRykd8Ln9RJ/98/ghABHz9TN8TRo2b6WimV64FmlVn17Ri6FgFU3xNt9TTEChq AcNg88eYryKsYpFwegGpwUlaUaaGh1m9OrTzcQy+klVfZWaVJ9Nw0keoGRGb8j4XjVpL8+2x OhXKrM1fzzb8JtAuSbuzZSQPDwQEI5CKKxp7zf76J21YeRrEW4WDznPyVcDTa+tz++q2S/Bp P4W98bXCBIuQgs2m+OflERv5c3Ojldp04/S4NEjXEYRWdiCxN7ca5iPml5gLtuvhJMSy36gl U6IW9kn30IWuSoBpTkgV7rLUEhh9Ms82VWW/h2TxL8enfx40PrfbDtWwqRID3WY8jLrjKfTd R3LW8BnUDNkG+c4FzvvGUs8AvuqxxyHbXAfDx9o/jXfPHVRmJVhSmd+hC3mcQ+4iX5bBPBPM oDqSoLt5w9GoQQ6gDVP2ZjTWqwSRMLzNr37rJjZ1pt0DCMMTbiYIUcrhX8eveCJtY7NGWNyx FCRkhxRuGcpwPmRVDwOl39MB3iTsRighiMnijkbLXiKoJ5CDVvX5yicNqYJPKh5MFXN1bvsB kmYiStMRbrD0HoY1kx5/VozBtc70OU0EB8Wrv9hZD+Ofp0T3KOr1RUHvCZoLURfFhSQ= In-Reply-To: <20250521043819-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 21/05/2025 10:39, Michael S. Tsirkin wrote: > On Wed, May 21, 2025 at 09:45:47AM +0200, Laurent Vivier wrote: >> On 21/05/2025 03:01, Jason Wang wrote: >>> On Tue, May 20, 2025 at 7:05 PM Laurent Vivier wrote: >>>> >>>> The `tx_may_stop()` logic stops TX queues if free descriptors >>>> (`sq->vq->num_free`) fall below the threshold of (2 + `MAX_SKB_FRAGS`). >>>> If the total ring size (`ring_num`) is not strictly greater than this >>>> value, queues can become persistently stopped or stop after minimal >>>> use, severely degrading performance. >>>> >>>> A single sk_buff transmission typically requires descriptors for: >>>> - The virtio_net_hdr (1 descriptor) >>>> - The sk_buff's linear data (head) (1 descriptor) >>>> - Paged fragments (up to MAX_SKB_FRAGS descriptors) >>>> >>>> This patch enforces that the TX ring size ('ring_num') must be strictly >>>> greater than (2 + MAX_SKB_FRAGS). This ensures that the ring is >>>> always large enough to hold at least one maximally-fragmented packet >>>> plus at least one additional slot. >>>> >>>> Reported-by: Lei Yang >>>> Signed-off-by: Laurent Vivier >>>> --- >>>> drivers/net/virtio_net.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>>> index e53ba600605a..866961f368a2 100644 >>>> --- a/drivers/net/virtio_net.c >>>> +++ b/drivers/net/virtio_net.c >>>> @@ -3481,6 +3481,12 @@ static int virtnet_tx_resize(struct virtnet_info *vi, struct send_queue *sq, >>>> { >>>> int qindex, err; >>>> >>>> + if (ring_num <= 2+MAX_SKB_FRAGS) { >>> >>> Nit: space is probably needed around "+" >> >> I agree, but I kept the original syntax used everywhere in the file. It >> eases the search of the value in the file. > > > it's a mixed bag: > > drivers/net/virtio_net.c: struct scatterlist sg[MAX_SKB_FRAGS + 2]; > drivers/net/virtio_net.c: struct scatterlist sg[MAX_SKB_FRAGS + 2]; > drivers/net/virtio_net.c: if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) { > drivers/net/virtio_net.c: if (sq->vq->num_free < 2+MAX_SKB_FRAGS) { > drivers/net/virtio_net.c: if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) { > drivers/net/virtio_net.c: if (*num_buf > MAX_SKB_FRAGS + 1) > drivers/net/virtio_net.c: if (unlikely(num_skb_frags == MAX_SKB_FRAGS)) { > drivers/net/virtio_net.c: if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) { > drivers/net/virtio_net.c: if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) { > drivers/net/virtio_net.c: vi->big_packets_num_skbfrags = guest_gso ? MAX_SKB_FRAGS : DIV_ROUND_UP(mtu, PAGE_SIZE); > > > we should fix it all. I think MAX_SKB_FRAGS + 2 is also cleaner than the > weird 2 + syntax. OK, I'm going to add a patch that will cleanup all this stuff. Thanks, Laurent > > > >>> >>>> + netdev_err(vi->dev, "tx size (%d) cannot be smaller than %d\n", >>>> + ring_num, 2+MAX_SKB_FRAGS); >>> >>> And here. >>> >>>> + return -EINVAL; >>>> + } >>>> + >>>> qindex = sq - vi->sq; >>>> >>>> virtnet_tx_pause(vi, sq); >>>> -- >>>> 2.49.0 >>>> >>> >>> Other than this. >>> >>> Acked-by: Jason Wang >>> >>> (Maybe we can proceed on don't stall if we had at least 1 left if >>> indirect descriptors are supported). >> >> But in this case, how to know when to stall the queue? >> >> Thank, >> Laurent >>> >>> Thanks >>> >