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 B693015E5DC; Wed, 14 Jan 2026 01:09:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768352990; cv=none; b=gerRHmmSWfeaJtLH7R9uCiGXRNoBxumG5vsiUSxzOT3a/g56H91wgM28+uuGcUjqNPIQTD39JZdDEuYTE6go8ouY1RYcioaCeZBlluqx43blieQI/XAjKEAxDTfY7Ke2TJ11qi9WcnvdsTdpgzri/XI1KQIjvNfSkswzaY91NPU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768352990; c=relaxed/simple; bh=FhTE2O81vVOc5m/6D5KI8Ud3LAbeCf+yg7dqhY6WG68=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=aqdBAaHwjBoDgQJ3dBT5wwEcIMJNykyrkn3jzyUJFXz6Xx/qLQQO0J+d9HuZbKagxHhHlx7eYbwbicgkexiXR1eKLnop/2Kw0bbXlL3QSn0wNuYkL2RX92XA5wfsO4yet250jnS1O4FBzWZworH8hf+UlyENSF0t2p4dJMbcmEE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RKStq6y3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RKStq6y3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BB7DC116C6; Wed, 14 Jan 2026 01:09:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768352990; bh=FhTE2O81vVOc5m/6D5KI8Ud3LAbeCf+yg7dqhY6WG68=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=RKStq6y3WT2H4tBiUmrgERKeiP8a4xid8VrfXFdZdPbyCr2o0LhEc6qW/a/5ClxXO zxtMjhf790lOIqQ/iWzwaCXFQUBeeYlcwCPWKKE5m+LQinXlKMYSAiEBpVBKjzzm1F raulX2TO2qo2EWBlnJISWJrD6D3SUAaYsuLTu9TOhHIWDeGvxHHhM+AdndBOm8esck oS6a1E6Q5Fl9T/46lP2PHfua2gsMuJrpINkTs6ePSf7R7i/qccKHaIctZmdY7169ei lIAhRxLR8n43a3/V5vYRPoILHi2se1pmRreq/YDXkEzgMKgRybmaKjDQ7h8ljtO7ES 2TMaAItMfuasw== Date: Tue, 13 Jan 2026 17:09:48 -0800 From: Jakub Kicinski To: Haiyang Zhang Cc: Haiyang Zhang , "linux-hyperv@vger.kernel.org" , "netdev@vger.kernel.org" , KY Srinivasan , Wei Liu , Dexuan Cui , Long Li , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , Konstantin Taranov , Simon Horman , Erni Sri Satya Vennela , Shradha Gupta , Saurabh Sengar , Aditya Garg , Dipayaan Roy , Shiraz Saleem , "linux-kernel@vger.kernel.org" , "linux-rdma@vger.kernel.org" , Paul Rosswurm Subject: Re: [EXTERNAL] Re: [PATCH V2,net-next, 1/2] net: mana: Add support for coalesced RX packets on CQE Message-ID: <20260113170948.1d6fbdaf@kernel.org> In-Reply-To: References: <1767732407-12389-1-git-send-email-haiyangz@linux.microsoft.com> <1767732407-12389-2-git-send-email-haiyangz@linux.microsoft.com> <20260109175610.0eb69acb@kernel.org> <20260112172146.04b4a70f@kernel.org> 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 Tue, 13 Jan 2026 15:13:24 +0000 Haiyang Zhang wrote: > > > I get that. What is the logic for combining 4 packets into a single > > > completion? How does it work? Your commit message mentions "regression > > > on latency" - what is the bound on that regression? > > > > When we received CQE type CQE_RX_COALESCED_4, it's a coalesced CQE. And in > > the CQE OOB, there is an array with 4 PPI elements, with each pkt's length: > > oob->ppi[i].pkt_len. > > > > So we read the related WQE and the DMA buffers for the RX pkt payloads, up > > to 4. > > But, if the coalesced pkts <4, the pkt_len will be 0 after the last pkt, > > so we know when to stop reading the WQEs. > > And, the coalescing can add up to 2 microseconds into one-way latency. I am asking you how the _device_ (hypervisor?) decides when to coalesce and when to send a partial CQE (<4 packets in 4 pkt CQE). You are using the coalescing uAPI, so I'm trying to make sure this is the correct API. CQE configuration can also be done via ringparam.