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 X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 AE76CC07E9B for ; Wed, 21 Jul 2021 03:30:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 75CDE61178 for ; Wed, 21 Jul 2021 03:30:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231404AbhGUCtc (ORCPT ); Tue, 20 Jul 2021 22:49:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:58372 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231394AbhGUCtc (ORCPT ); Tue, 20 Jul 2021 22:49:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626838208; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=k05rJ04IU9dEG8xbaeJSAOzZNy8JTOVIRfo0vVOjOCg=; b=UkrQAPY/jJJBP7IhjgyWmTvbkFxAnwKlONODMGHTpjbG14cFAtDREsLYAMEWKPzvUbCaeu qkdS4IMQJXcDLPOYDhttPJMTOLlGxf6nN2Bs5KMyFmoNntNru5d8IcKht8AMnnGubPHYYt kNnJPHioxad/MoAhuD6i3+HpGkXR+tA= Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-525-WuVumG3EMOKW-drnYxPaNQ-1; Tue, 20 Jul 2021 23:30:07 -0400 X-MC-Unique: WuVumG3EMOKW-drnYxPaNQ-1 Received: by mail-pg1-f200.google.com with SMTP id z14-20020a63e54e0000b029022cae6eb6eeso636113pgj.12 for ; Tue, 20 Jul 2021 20:30:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=k05rJ04IU9dEG8xbaeJSAOzZNy8JTOVIRfo0vVOjOCg=; b=tcbe5ZRLuNipBd8q81h4zNc/0n9LrMnCW7laMiBuaacGQTTbhqRTAutsZPcBg7dRgn 3aS20QrH4a8bzyLKROSsYn0LuLwVIyYAQuk5EbtIwrZ+b4BbtlhasJm31o/PbP3FoKBf oBbGsxJsZ+i29Q/IRySRmAQXEAHzjhFxUGVpjCj/X687awyGpVdswkEe8bKU/ugSf801 LpTd2S3CAKlpDKqJpKX3Reny0dEG7dBD0hOrzZI6IpcKejXYK128vg5GvcgnfNtttRNt 2pRHgAH954hVcPWZasY/4RXkwHK2BpeCofrc6DoMeFvEA4IkWjPEZnb43ndwx9r/kE2R apWQ== X-Gm-Message-State: AOAM532gg605O/9BpFr8NfrcxUwl8P9lgxv/n/rOEEeeLMamTOZSzomq H/HOvc323oLQ+DOk+u/k1L8LIOb3DaT3Once4MKeK9qIPf+Jgj10XFA6KZdKaJDky/vxi2ZNRdd mgEMoup9xfrOTdYeFoefrYmU= X-Received: by 2002:a17:90a:17eb:: with SMTP id q98mr1637495pja.183.1626838206005; Tue, 20 Jul 2021 20:30:06 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyESsAEWCDLWvcTfXZOmxCYVAakGzjamKbkQkgTTty1VuN8o5+HezI8WKMk3qXoufEpH/sFbw== X-Received: by 2002:a17:90a:17eb:: with SMTP id q98mr1637476pja.183.1626838205751; Tue, 20 Jul 2021 20:30:05 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id w14sm30244343pgo.75.2021.07.20.20.30.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Jul 2021 20:30:05 -0700 (PDT) Subject: Re: [RFC 0/3] cpuidle: add poll_source API and virtio vq polling To: Stefan Hajnoczi , linux-kernel@vger.kernel.org Cc: Daniel Lezcano , Stefano Garzarella , Ming Lei , "Michael S . Tsirkin" , Marcelo Tosatti , Jens Axboe , linux-block@vger.kernel.org, "Rafael J. Wysocki" , virtualization@lists.linux-foundation.org, linux-pm@vger.kernel.org, Christoph Hellwig References: <20210713161906.457857-1-stefanha@redhat.com> From: Jason Wang Message-ID: <1008dee4-fce1-2462-1520-f5432bc89a07@redhat.com> Date: Wed, 21 Jul 2021 11:29:55 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210713161906.457857-1-stefanha@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 在 2021/7/14 上午12:19, Stefan Hajnoczi 写道: > These patches are not polished yet but I would like request feedback on this > approach and share performance results with you. > > Idle CPUs tentatively enter a busy wait loop before halting when the cpuidle > haltpoll driver is enabled inside a virtual machine. This reduces wakeup > latency for events that occur soon after the vCPU becomes idle. > > This patch series extends the cpuidle busy wait loop with the new poll_source > API so drivers can participate in polling. Such polling-aware drivers disable > their device's irq during the busy wait loop to avoid the cost of interrupts. > This reduces latency further than regular cpuidle haltpoll, which still relies > on irqs. > > Virtio drivers are modified to use the poll_source API so all virtio device > types get this feature. The following virtio-blk fio benchmark results show the > improvement: > > IOPS (numjobs=4, iodepth=1, 4 virtqueues) > before poll_source io_poll > 4k randread 167102 186049 (+11%) 186654 (+11%) > 4k randwrite 162204 181214 (+11%) 181850 (+12%) > 4k randrw 159520 177071 (+11%) 177928 (+11%) > > The comparison against io_poll shows that cpuidle poll_source achieves > equivalent performance to the block layer's io_poll feature (which I > implemented in a separate patch series [1]). > > The advantage of poll_source is that applications do not need to explicitly set > the RWF_HIPRI I/O request flag. The poll_source approach is attractive because > few applications actually use RWF_HIPRI and it takes advantage of CPU cycles we > would have spent in cpuidle haltpoll anyway. > > The current series does not improve virtio-net. I haven't investigated deeply, > but it is possible that NAPI and poll_source do not combine. See the final > patch for a starting point on making the two work together. > > I have not tried this on bare metal but it might help there too. The cost of > disabling a device's irq must be less than the savings from avoiding irq > handling for this optimization to make sense. > > [1] https://lore.kernel.org/linux-block/20210520141305.355961-1-stefanha@redhat.com/ Hi Stefan: Some questions: 1) What's the advantages of introducing polling at virtio level instead of doing it at each subsystems? Polling in virtio level may only work well if all (or most) of the devices are virtio 2) What's the advantages of using cpuidle instead of using a thread (and leverage the scheduler)? 3) Any reason it's virtio_pci specific not a general virtio one? Thanks (Btw, do we need to cc scheduler guys?) > > Stefan Hajnoczi (3): > cpuidle: add poll_source API > virtio: add poll_source virtqueue polling > softirq: participate in cpuidle polling > > drivers/cpuidle/Makefile | 1 + > drivers/virtio/virtio_pci_common.h | 7 ++ > include/linux/interrupt.h | 2 + > include/linux/poll_source.h | 53 +++++++++++++++ > include/linux/virtio.h | 2 + > include/linux/virtio_config.h | 2 + > drivers/cpuidle/poll_source.c | 102 +++++++++++++++++++++++++++++ > drivers/cpuidle/poll_state.c | 6 ++ > drivers/virtio/virtio.c | 34 ++++++++++ > drivers/virtio/virtio_pci_common.c | 86 ++++++++++++++++++++++++ > drivers/virtio/virtio_pci_modern.c | 2 + > kernel/softirq.c | 14 ++++ > 12 files changed, 311 insertions(+) > create mode 100644 include/linux/poll_source.h > create mode 100644 drivers/cpuidle/poll_source.c >