From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 61A6746FDD; Mon, 8 Dec 2025 11:06:54 +0100 (CET) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id F0B3640280; Mon, 8 Dec 2025 11:06:53 +0100 (CET) Received: from inbox.dpdk.org (inbox.dpdk.org [95.142.172.178]) by mails.dpdk.org (Postfix) with ESMTP id 22E674003C for ; Mon, 8 Dec 2025 11:06:53 +0100 (CET) Received: by inbox.dpdk.org (Postfix, from userid 33) id 020D346FE2; Mon, 8 Dec 2025 11:06:52 +0100 (CET) From: bugzilla@dpdk.org To: dev@dpdk.org Subject: [DPDK/ethdev Bug 1848] Using maximum RX descriptor causes 100% imiss Date: Mon, 08 Dec 2025 10:06:52 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: DPDK X-Bugzilla-Component: ethdev X-Bugzilla-Version: 22.11 X-Bugzilla-Keywords: X-Bugzilla-Severity: major X-Bugzilla-Who: canary.overflow@gmail.com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: Normal X-Bugzilla-Assigned-To: dev@dpdk.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 X-Bugzilla-URL: http://bugs.dpdk.org/ Auto-Submitted: auto-generated X-Auto-Response-Suppress: All MIME-Version: 1.0 X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org http://bugs.dpdk.org/show_bug.cgi?id=3D1848 Bug ID: 1848 Summary: Using maximum RX descriptor causes 100% imiss Product: DPDK Version: 22.11 Hardware: x86 OS: Linux Status: UNCONFIRMED Severity: major Priority: Normal Component: ethdev Assignee: dev@dpdk.org Reporter: canary.overflow@gmail.com Target Milestone: --- I have a server using the following setup: NIC card:MT27800 (ConnectX-5) DPDK version: 22.11 driver: mlx5_core version: 5.7-1.0.2 firmware: 16.35.4506 (MT_0000000011) Issue: 100% imiss was observed when I tried to use rx_desc=3D32768 (32768 i= s the maximum supported by the NIC) testpmd command: dpdk-testpmd -l 1-10 -n 4 -a 0000:45:00.0,rxq_comp_en=3D1,rxq_pkt_pad_en=3D= 1 -=E2=80=93 -i =E2=80=93-max_pkt_len=3D4096 =E2=80=93-rxq=3D8 -=E2=80=93txq=3D8 --nb_cores= =3D8 -=E2=80=93rxd=3D32768 -=E2=80=93enable_drop_en =E2=80=93-enable_scatter After tracing through the DPDK source code, I came across this code: drivers/net/mlx5/mlx5_devx.c /* * For vectorized Rx, it must not be doubled in order to * make cq_ci and rq_ci aligned. */ if (mlx5_rxq_check_vec_support(rxq_data) < 0) cqe_n *=3D 2; The above code doubles the amount of CQE for non-vectorized RX and I'm not = sure if this will affect other drivers or the NIC firmware. In addition, I also = saw a few functions where `cqe_n` was assigned to a uint16_t which will cause overflow (e.g. rxq_sync_cq(), mlx5_rx_err_handle()). I further confirmed that imiss is not 100% in vectorized mode (MTU=3D1500) = but 100% imiss in non-vectorized mode (MTU=3D4096) where rx_desc=3D32768. I have also tried upgrading my setup to use the latest version of DPDK library(25.11) but same observations were made. As I am not very familiar with the MLX5 driver, can someone assist to check= if the doubling of rx desc from 32768 to 65536 in non-vectorized mode will res= ult in other issues in the NIC firmware or driver? --=20 You are receiving this mail because: You are the assignee for the bug.=