From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0415C6FD1C for ; Sat, 25 Mar 2023 05:43:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231810AbjCYFmz (ORCPT ); Sat, 25 Mar 2023 01:42:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229441AbjCYFmy (ORCPT ); Sat, 25 Mar 2023 01:42:54 -0400 Received: from nbd.name (nbd.name [46.4.11.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5AC481A48C; Fri, 24 Mar 2023 22:42:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=nbd.name; s=20160729; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=elBC7x8BCDuYhJTGwQV3bWcb2ZYFxDKqqBJRBK7oPXA=; b=MfYdNUgeY+5US8ue8eoYcRVIyp vlkWGh2XrS2isG+R+p58i3KZxlnLWqJjzhedN9Jf7elWGTXCi6YBUYXreMyqPgI+DY5Z1mfZbupQM 0R8dKbj7amqnvFhHKCV3RLxq7oqHwLKThyDEZnC0Xe9JiSsvVmtMq3xxx41IxE15K1ak=; Received: from p54ae9730.dip0.t-ipconnect.de ([84.174.151.48] helo=nf.local) by ds12 with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1pfwfr-006bjW-Us; Sat, 25 Mar 2023 06:42:44 +0100 Message-ID: <2ef8ab92-3670-61a1-384d-b827865447ca@nbd.name> Date: Sat, 25 Mar 2023 06:42:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH net-next] net/core: add optional threading for backlog processing Content-Language: en-US To: Jakub Kicinski Cc: netdev@vger.kernel.org, Jonathan Corbet , "David S. Miller" , Eric Dumazet , Paolo Abeni , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20230324171314.73537-1-nbd@nbd.name> <20230324102038.7d91355c@kernel.org> <2d251879-1cf4-237d-8e62-c42bb4feb047@nbd.name> <20230324104733.571466bc@kernel.org> <20230324201951.75eabe1f@kernel.org> From: Felix Fietkau In-Reply-To: <20230324201951.75eabe1f@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 25.03.23 04:19, Jakub Kicinski wrote: > On Fri, 24 Mar 2023 18:57:03 +0100 Felix Fietkau wrote: >> >> It can basically be used to make RPS a bit more dynamic and >> >> configurable, because you can assign multiple backlog threads to a set >> >> of CPUs and selectively steer packets from specific devices / rx queues >> > >> > Can you give an example? >> > >> > With the 4 CPU example, in case 2 queues are very busy - you're trying >> > to make sure that the RPS does not end up landing on the same CPU as >> > the other busy queue? >> >> In this part I'm thinking about bigger systems where you want to have a >> group of CPUs dedicated to dealing with network traffic without >> assigning a fixed function (e.g. NAPI processing or RPS target) to each >> one, allowing for more dynamic processing. > > I tried the threaded NAPI on larger systems and helped others try, > and so far it's not been beneficial :( Even the load balancing > improvements are not significant enough to use it, and there > is a large risk of scheduler making the wrong decision. > > Hence my questioning - I'm trying to understand what you're doing > differently. I didn't actually run any tests on bigger systems myself, so I don't know how to tune it for those. >> >> to them and allow the scheduler to take care of the rest. >> > >> > You trust the scheduler much more than I do, I think :) >> >> In my tests it brings down latency (both avg and p99) considerably in >> some cases. I posted some numbers here: >> https://lore.kernel.org/netdev/e317d5bc-cc26-8b1b-ca4b-66b5328683c4@nbd.name/ > > Could you provide the full configuration for this test? > In non-threaded mode the RPS is enabled to spread over remaining > 3 cores? In this test I'm using threaded NAPI and backlog_threaded without any fixed core assignment. - Felix