From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AEC8F134A7; Wed, 5 Jul 2023 18:11:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B9DC0C433C7; Wed, 5 Jul 2023 18:11:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1688580681; bh=KweOEW8GfMOMNLvHYMkARFoxe20foH7IJPTc8uzro5U=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=k7x8QXaEeLGFcfy29GO40jjHONBbBUk60hI6vcX9hBiOzahQ2oAgXZP/ie9blNMwR 4okF9/Avx3zPKsPFurywdGIqudclJ8+nLUw2A3d3yiJe3dd9RpvowwramVZ4JNZ+4K 5Fg+xyvIEQbHFzc5RJSe1YIUofsyfOs0w1JwfOmFJ7Znf/GQmUroiRsgTuFyw3Cg4f LjrVLRshCbLLJWSXRZkzW+Gg92RClQNWksjIpm1yRMUsximrO4+0Q1nT1C/g9PIBIf FSvHgsdgotG22s3k8274ZQJdtrICBV53CtJn9O78yLCVvkDsePdPUkWcenjjHURgKe hSNTTySw6908A== Date: Wed, 5 Jul 2023 11:11:19 -0700 From: Jakub Kicinski To: Wei Fang Cc: Andrew Lunn , "davem@davemloft.net" , "edumazet@google.com" , "pabeni@redhat.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "hawk@kernel.org" , "john.fastabend@gmail.com" , Shenwei Wang , Clark Wang , "netdev@vger.kernel.org" , dl-linux-imx , "linux-kernel@vger.kernel.org" , "bpf@vger.kernel.org" Subject: Re: [PATCH net 3/3] net: fec: increase the size of tx ring and update thresholds of tx ring Message-ID: <20230705111119.07c3dee3@kernel.org> In-Reply-To: References: <20230704082916.2135501-1-wei.fang@nxp.com> <20230704082916.2135501-4-wei.fang@nxp.com> <0443a057-767f-4f9c-afd2-37d26b606d74@lunn.ch> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 5 Jul 2023 06:20:26 +0000 Wei Fang wrote: > > > In addtion, this patch also updates the tx_stop_threshold and the > > > tx_wake_threshold of the tx ring. In previous logic, the value of > > > tx_stop_threshold is 217, however, the value of tx_wake_threshold is > > > 147, it does not make sense that tx_wake_threshold is less than > > > tx_stop_threshold. > > > > What do these actually mean? I could imagine that as the ring fills you don't > > want to stop until it is 217/512 full. There is then some hysteresis, such that it > > has to drop below 147/512 before more can be added? > > > You must have misunderstood, let me explain more clearly, the queue will be > stopped when the available BDs are less than tx_stop_threshold (217 BDs). And > the queue will be waked when the available BDs are greater than tx_wake_threshold > (147 BDs). So in most cases, the available BDs are greater than tx_wake_threshold > when the queue is stopped, the only effect is to delay packet sending. > In my opinion, tx_wake_threshold should be greater than tx_stop_threshold, we > should stop queue when the available BDs are not enough for a skb to be attached. > And wake the queue when the available BDs are sufficient for a skb. But you shouldn't restart the queue for a single packet either. Restarting for a single packet wastes CPU cycles as there will be much more stop / start operations. Two large packets seem like the absolute minimum reasonable wake threshold. Setting tx_stop_threshold to MAX_SKB_FRAGS doesn't seem right either, as you won't be able to accept a full TSO frame. Please split the change, the netdev_err_once() should be one patch and then the change to wake thresh a separate one. -- pw-bot: cr