From patchwork Wed Jan 20 03:34:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wei Wang X-Patchwork-Id: 367677 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-21.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT, USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A436FC433E0 for ; Wed, 20 Jan 2021 03:38:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AA6922573 for ; Wed, 20 Jan 2021 03:38:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731548AbhATDhs (ORCPT ); Tue, 19 Jan 2021 22:37:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729021AbhATDfi (ORCPT ); Tue, 19 Jan 2021 22:35:38 -0500 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BFECDC061575 for ; Tue, 19 Jan 2021 19:34:57 -0800 (PST) Received: by mail-qv1-xf49.google.com with SMTP id x17so21751962qvo.23 for ; Tue, 19 Jan 2021 19:34:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=iJ2g1y3GZkvZ9flORg/0AJGpx/1eHjaoEC109grJ/g4=; b=WfN7XP/jHhByutpgFsDycr4mXqWOppqGXuMjZ4EJGf1QCuBVsiEbJUoZRWoF/grZbH k5+A8kCvU7pJeohFNAPQbE1qGUdsrb94JpLNH7SgKFPIYHedxcWyI29blAG0fzntx8Oa EYEh9A6R0vyfYRlsR5BKGmGrhl4mq49+3H43N6dbgxh2E3G8GOaOwK59MWkMQP+79BO1 /s44LB35AcaWXkBSb/DuJzDMAAP5g2K+VSFqdHZ7pHMrLhZkdNwTa2mASrjOgozppxDv JILCM+dKKKpW+mwSYB1mK1Vw9m9jM85mhqXGhvQcV4A6+nkixk9NZSSsw8WoHo4drbVf TWBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=iJ2g1y3GZkvZ9flORg/0AJGpx/1eHjaoEC109grJ/g4=; b=S7oJQkzYzbI7yn6j46flkq4PFXEpDh9TdYRCHyA/L2fozlIcOpTnzGMLqyjrZnRfJZ gqAR7Jp6DW6eNToid+vEaWYP13GXPbX8uMvsN9QhBxy2h6Cfh66wDHY/enuhvFYN18Hv ABlBkfjPDtFs5qJ7Dp/JSQar6WBksTo0QRM0AiSo+CEuSVHcE1/NLlBZgTZeuPPo4F63 G26G9wAdCcSNZXWpMKD1vUPKdVhPsAPiucDjthZkcTk4ySyV2w+j2QVeFiAhOgH93Wjc HY2xQ9PtW2JSeyMF2tKY0ps7UaJWehcBJMg5XgvnNUm9QjhIfKmAmswPhKfPccaxWscI koAA== X-Gm-Message-State: AOAM531BCSeoJ2aUngTW0FCorqwGW/b4qUbhqyBxIMbaIzk24pQNkp4l F+MO5/SyTAoIiXwbQ4ogKJLBK3BNPkI= X-Google-Smtp-Source: ABdhPJyxBWxkMCI4irOWmNPO8hptjRHagLzFfZxs82+aUSa/nUnjZA6FsUO8jpPZcdpaUbrDOC00FyZwQAo= Sender: "weiwan via sendgmr" X-Received: from weiwan.svl.corp.google.com ([2620:15c:2c4:201:1ea0:b8ff:fe75:cf08]) (user=weiwan job=sendgmr) by 2002:ad4:4ae2:: with SMTP id cp2mr7885787qvb.50.1611113696851; Tue, 19 Jan 2021 19:34:56 -0800 (PST) Date: Tue, 19 Jan 2021 19:34:52 -0800 Message-Id: <20210120033455.4034611-1-weiwan@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.30.0.284.gd98b1dd5eaa7-goog Subject: [PATCH net-next v7 0/3] implement kthread based napi poll From: Wei Wang To: David Miller , netdev@vger.kernel.org, Jakub Kicinski Cc: Eric Dumazet , Paolo Abeni , Hannes Frederic Sowa , Felix Fietkau , Alexander Duyck Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The idea of moving the napi poll process out of softirq context to a kernel thread based context is not new. Paolo Abeni and Hannes Frederic Sowa have proposed patches to move napi poll to kthread back in 2016. And Felix Fietkau has also proposed patches of similar ideas to use workqueue to process napi poll just a few weeks ago. The main reason we'd like to push forward with this idea is that the scheduler has poor visibility into cpu cycles spent in softirq context, and is not able to make optimal scheduling decisions of the user threads. For example, we see in one of the application benchmark where network load is high, the CPUs handling network softirqs has ~80% cpu util. And user threads are still scheduled on those CPUs, despite other more idle cpus available in the system. And we see very high tail latencies. In this case, we have to explicitly pin away user threads from the CPUs handling network softirqs to ensure good performance. With napi poll moved to kthread, scheduler is in charge of scheduling both the kthreads handling network load, and the user threads, and is able to make better decisions. In the previous benchmark, if we do this and we pin the kthreads processing napi poll to specific CPUs, scheduler is able to schedule user threads away from these CPUs automatically. And the reason we prefer 1 kthread per napi, instead of 1 workqueue entity per host, is that kthread is more configurable than workqueue, and we could leverage existing tuning tools for threads, like taskset, chrt, etc to tune scheduling class and cpu set, etc. Another reason is if we eventually want to provide busy poll feature using kernel threads for napi poll, kthread seems to be more suitable than workqueue. Furthermore, for large platforms with 2 NICs attached to 2 sockets, kthread is more flexible to be pinned to different sets of CPUs. In this patch series, I revived Paolo and Hannes's patch in 2016 and made modifications. Then there are changes proposed by Felix, Jakub, Paolo and myself on top of those, with suggestions from Eric Dumazet. In terms of performance, I ran tcp_rr tests with 1000 flows with various request/response sizes, with RFS/RPS disabled, and compared performance between softirq vs kthread vs workqueue (patchset proposed by Felix Fietkau). Host has 56 hyper threads and 100Gbps nic, 8 rx queues and only 1 numa node. All threads are unpinned. req/resp QPS 50%tile 90%tile 99%tile 99.9%tile softirq 1B/1B 2.75M 337us 376us 1.04ms 3.69ms kthread 1B/1B 2.67M 371us 408us 455us 550us workq 1B/1B 2.56M 384us 435us 673us 822us softirq 5KB/5KB 1.46M 678us 750us 969us 2.78ms kthread 5KB/5KB 1.44M 695us 789us 891us 1.06ms workq 5KB/5KB 1.34M 720us 905us 1.06ms 1.57ms softirq 1MB/1MB 11.0K 79ms 166ms 306ms 630ms kthread 1MB/1MB 11.0K 75ms 177ms 303ms 596ms workq 1MB/1MB 11.0K 79ms 180ms 303ms 587ms When running workqueue implementation, I found the number of threads used is usually twice as much as kthread implementation. This probably introduces higher scheduling cost, which results in higher tail latencies in most cases. I also ran an application benchmark, which performs fixed qps remote SSD read/write operations, with various sizes. Again, both with RFS/RPS disabled. The result is as follows: op_size QPS 50%tile 95%tile 99%tile 99.9%tile softirq 4K 572.6K 385us 1.5ms 3.16ms 6.41ms kthread 4K 572.6K 390us 803us 2.21ms 6.83ms workq 4k 572.6K 384us 763us 3.12ms 6.87ms softirq 64K 157.9K 736us 1.17ms 3.40ms 13.75ms kthread 64K 157.9K 745us 1.23ms 2.76ms 9.87ms workq 64K 157.9K 746us 1.23ms 2.76ms 9.96ms softirq 1M 10.98K 2.03ms 3.10ms 3.7ms 11.56ms kthread 1M 10.98K 2.13ms 3.21ms 4.02ms 13.3ms workq 1M 10.98K 2.13ms 3.20ms 3.99ms 14.12ms In this set of tests, the latency is predominant by the SSD operation. Also, the user threads are much busier compared to tcp_rr tests. We have to pin the kthreads/workqueue threads to limit to a few CPUs, to not disturb user threads, and provide some isolation. Changes since v6: Added memory barrier in napi_set_threaded(). Changed /sys/class/net//thread to a ternary value. Change dev->threaded to a bit instead of bool. Changes since v5: Removed ASSERT_RTNL() from napi_set_threaded() and removed rtnl_lock() operation from napi_enable(). Changes since v4: Recorded the threaded setting in dev and restore it in napi_enable(). Changes since v3: Merged and rearranged patches in a logical order for easier review. Changed sysfs control to be per device. Changes since v2: Corrected typo in patch 1, and updated the cover letter with more detailed and updated test results. Changes since v1: Replaced kthread_create() with kthread_run() in patch 5 as suggested by Felix Fietkau. Changes since RFC: Renamed the kthreads to be napi/- in patch 5 as suggested by Hannes Frederic Sowa. Felix Fietkau (1): net: extract napi poll functionality to __napi_poll() Wei Wang (2): net: implement threaded-able napi poll loop support net: add sysfs attribute to control napi threaded mode include/linux/netdevice.h | 21 ++-- net/core/dev.c | 200 ++++++++++++++++++++++++++++++++++++-- net/core/net-sysfs.c | 68 +++++++++++++ 3 files changed, 265 insertions(+), 24 deletions(-)