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 A9D4B45A9D for ; Wed, 2 Oct 2024 17:29:23 +0200 (CEST) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 69C704025E; Wed, 2 Oct 2024 17:29:23 +0200 (CEST) Received: from mail-pj1-f51.google.com (mail-pj1-f51.google.com [209.85.216.51]) by mails.dpdk.org (Postfix) with ESMTP id 343BE4025C for ; Wed, 2 Oct 2024 17:29:21 +0200 (CEST) Received: by mail-pj1-f51.google.com with SMTP id 98e67ed59e1d1-2e053f42932so5000586a91.0 for ; Wed, 02 Oct 2024 08:29:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20230601.gappssmtp.com; s=20230601; t=1727882960; x=1728487760; darn=dpdk.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=MtnY1gIi/Lk7GvVe/l0UIYp3pjMuo1tiGh2rD4tNBsc=; b=mnMz0zUgtIjK4kpcd0HLTVtJfHQ2NdHZh+lf7JP1HHm83eQ2keYIowCRYhu46LZN4C PHFpSwMS1oiWsZjEkRkDAGMmXD1NHihq3JR+WeymmZG93hF5ebtSscsUwas3mxDNmQGQ 6HE0cw5/TroxTIUWhHXX8QapuMSXA1ZaMySst6BIiO0whieF/rlB9FPwKZO5hdkk4BaE FwCXghT1lYLw+mt7u4NNqJMRGeRW0F0dfxNOA8GwD+9SeL+mOCwSmvoV8aJupud0e5Bi AGFIQlmrZDqoU0eo3nvStHqkGnManzkQJU2kW7SOwDIVLDdt/Q2tkpwxL7vSJoroJNOH lwMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727882960; x=1728487760; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=MtnY1gIi/Lk7GvVe/l0UIYp3pjMuo1tiGh2rD4tNBsc=; b=Phg1vIdy2Wh/acYVsOcMYrmL5Xqcf2iLoseHLKMCJnQOb5qQhd/tlN4coNYdwTdcy1 C/sAvYXG0irnp8X07qu+/ChJGoaKo0dNjg4caqz8WvStZ3RTLL5SMcRX5wM9UzWoQRAA C6t3Yp3fa++1Oh0oMQMYR2BNO2Iq4Mtw6SlvWuG6b9D2GCkcoBCPsK1r7GnNHaGK6AvC 0j9WiK1lUqimEwcFbWSTFZa4uOSO7VNdviRkHS6/57ZE4+yjheFUGDyAZltidekexVQ/ rVOae5/8X13oIBui4JBfbjPYTCdm2BPpcNK5i9w39PvS1Qac3dmXz6xUyPU9zEoT0jUh fwEA== X-Gm-Message-State: AOJu0YwJLHsztXuZZplz2xv234KpBfxc/w9JknhbX9DLmtYUtm5Qio12 Q3CoBz56coXTlN0iX+zfDPwTqnGZZ2QYtPR+UpBzB13bXldKZTLdS2qI2JkbxwTFZrChQ3YGJ7l j X-Google-Smtp-Source: AGHT+IF7Mw07gshBKlijskHp/IhRef3zcUZ0qYCXxVPlBqZb86RaXGf7sp6RSH+M/LjWYX015DsqKA== X-Received: by 2002:a17:90b:3b8c:b0:2d8:8f24:bd88 with SMTP id 98e67ed59e1d1-2e18466dac6mr4199318a91.14.1727882960096; Wed, 02 Oct 2024 08:29:20 -0700 (PDT) Received: from hermes.local (204-195-96-226.wavecable.com. [204.195.96.226]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e18f541865sm1714651a91.12.2024.10.02.08.29.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Oct 2024 08:29:19 -0700 (PDT) Date: Wed, 2 Oct 2024 08:29:18 -0700 From: Stephen Hemminger To: Mikael R Carlsson Cc: "users@dpdk.org" Subject: Re: Relation between DPDK queue and descriptors Message-ID: <20241002082918.0207a447@hermes.local> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: users@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK usage discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: users-bounces@dpdk.org On Wed, 2 Oct 2024 15:21:45 +0000 Mikael R Carlsson wrote: > Hi experts! > > I have a hard time to finds a good documentation about the relation between DPDK TX queue and descriptors. > > Queue as in rte_eth_tx_queue_setup > Descriptor as in rte_eth_dev_adjust_nb_rx_rx_desc > > We suspect we run out of descriptors in TX path, we are not sure here. We use more than one TX queue. Will we get more descriptors if we only use one single TX queue? Does anyone know if there is some good documentation regarding the TX queue and the descriptors? > > / Mikael > A typical driver has a hardware ring buffer between the driver and the hardware. One ring for transmit, and another for receive. The entries in the ring are hardware specific data structure called descriptors. Each descriptor usually has physical memory address, size, and flags. The number of Rx descriptors determines the number of unread frames the driver can hold. Too small, and you risk dropping packets; too large and under stress load the driver can end up buffering excessively causing latency (bufferbloat). Similar on Tx but less of a problem because typically the network is faster than the application can send packets.