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Miller" , Eric Dumazet , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , Stanislav Fomichev , Hao Luo , Jiri Olsa , Simon Horman , Toshiaki Makita , David Ahern , Toke Hoiland Jorgensen Cc: Tariq Toukan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Martin KaFai Lau , KP Singh , kernel-team References: <20251107102853.1082118-2-dtatulea@nvidia.com> <20251107102853.1082118-5-dtatulea@nvidia.com> <4eusyirzvomxwkzib5tqfyrcgjcxoplrsf7jctytvyvrfvi5fr@f3lvd5h2kb2p> <58b50903-7969-46bd-bd73-60629c00f057@kernel.org> Content-Language: en-US From: Dragos Tatulea In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR5P281CA0039.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f3::18) To CH3PR12MB8728.namprd12.prod.outlook.com (2603:10b6:610:171::12) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB8728:EE_|BL4PR12MB9533:EE_ X-MS-Office365-Filtering-Correlation-Id: 6ec50421-9a4f-43e2-e58d-08de31bff12b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016|921020; 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I was ignorant about the egress part of the program. >>> That did the trick. The drop happens before reaching the tx >>> queue of the second netdev and the mentioned code in devmem.c >>> is reached. >>> >>> Sender is xdp-trafficgen with 3 threads pushing enough on one RX queue >>> to saturate the CPU. >>> >>> Here's what I got: >>> >>> * before: >>> >>> eth2->eth3             16,153,328 rx/s         16,153,329 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,153,329 drop/s                0 drv_err/s         16.00 bulk-avg >>> eth2->eth3             16,152,538 rx/s         16,152,546 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,152,546 drop/s                0 drv_err/s         16.00 bulk-avg >>> eth2->eth3             16,156,331 rx/s         16,156,337 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,156,337 drop/s                0 drv_err/s         16.00 bulk-avg >>> >>> * after: >>> >>> eth2->eth3             16,105,461 rx/s         16,105,469 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,105,469 drop/s                0 drv_err/s         16.00 bulk-avg >>> eth2->eth3             16,119,550 rx/s         16,119,541 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,119,541 drop/s                0 drv_err/s         16.00 bulk-avg >>> eth2->eth3             16,092,145 rx/s         16,092,154 err,drop/s            0 xmit/s >>>    xmit eth2->eth3               0 xmit/s       16,092,154 drop/s                0 drv_err/s         16.00 bulk-avg >>> >>> So slightly worse... I don't fully trust the measurements though as I >>> saw the inverse situation in other tests as well: higher rate after the >>> patch. > > Remember that you are also removing some code (the > xdp_set_return_frame_no_direct and xdp_clear_return_frame_no_direct). > Thus, I was actually hoping we would see a higher rate after the patch. > This is why I wanted to see this XDP-redirect test, instead of the > page_pool micro-benchmark. > Right. This was mentioned in the initial message as well. I was also hoping to see an improvement... > >> I had a chance to re-run this on a more stable system and the conclusion >> is the same. Performance is ~2 % worse: >> >> * before: >> eth2->eth3        13,746,431 rx/s   13,746,471 err,drop/s 0 xmit/s >>    xmit eth2->eth3          0 xmit/s 13,746,471 drop/s     0 drv_err/s 16.00 bulk-avg >> >> * after: >> eth2->eth3        13,437,277 rx/s   13,437,259 err,drop/s 0 xmit/s >>    xmit eth2->eth3          0 xmit/s 13,437,259 drop/s     0 drv_err/s 16.00 bulk-avg >> >> After this experiment it doesn't seem like this direction is worth >> proceeding with... I was more optimistic at the start. > > I do think it is worth proceeding.  I will claim that your PPS results > are basically the same. Converting PPS number to nanosec per packet: > >  13,746,471 = (1/13746471*10^9) = 72.74 nanosec >  13,437,259 = (1/13437259*10^9) = 74.42 nanosec >  Difference is  = (74.42-72.75) =  1.67 nanosec > > In my experience it is very hard to find a system stable enough to > measure a 2 nanosec difference. As you also note you had to spend effort > finding a stable system.  Thus, I claim your results show no noticeable > performance impact. > Oh yes, converting to ns does bring a different perspective... > My only concern (based on your perf symbols) is that you might not be > testing the right/expected code path.  If mlx5 is running with a > page_pool memory mode that have elevated refcnf on the page, then we > will not be exercising the slower page_pool ptr_ring return path as much > as expected.  I guess, I have to do this experiment in my own testlab on > other NIC drivers that doesn't use elevated refcnt as default. > This part I don't get. I thought that the point was to measure the impact of the change on fastest path: recycle to cache. Are you saying that you would like to see the impact on the slowest path as well? Or would you like to see the impact for a mix of the two? Maybe mlx5 can be hacked into this mode for benchmarking. But not sure I understand your usecase. > >>>>> Toke (and I) will appreciate if you added code for this to xdp-bench. >>>> Supporting a --program-mode like 'redirect-cpu' does. >>>> >>>> >>> Ok. I will add it. >>> >> Added it here: >> https://github.com/xdp-project/xdp-tools/pull/532 >> > > Thanks, I'll take a look, and I'm sure Toke have opinions on the cmdline > options and the missing man-page update. > Oh forgot about man-page. Will wait for his PR comments. Thanks, Dragos