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=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 968C3C433ED for ; Tue, 13 Apr 2021 08:51:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C08A613AE for ; Tue, 13 Apr 2021 08:51:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243761AbhDMIvm (ORCPT ); Tue, 13 Apr 2021 04:51:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:45749 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229750AbhDMIvl (ORCPT ); Tue, 13 Apr 2021 04:51:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618303881; 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=jCposirTbsc74EjO13nDclHit9p5R2qmCz4hXiIKwZg=; b=eiZSHu4DbdnLnSkFziOK1Ar9+MS0vTZSzfAnOSVTNblufMS5fnpCA+ytUyq5bRKXc5D5zH 5DS4QgGTZrU9HJiWdw+1ym/gTguo9tkY8VappT+MdEaqdco4JGVWzJL4bftpBxhB+zqoJl Vesej0T7R+pOzRX9Dh56fWueJheA3sY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-495-VUhAiWeYM1WfVsiK56hWtg-1; Tue, 13 Apr 2021 04:51:17 -0400 X-MC-Unique: VUhAiWeYM1WfVsiK56hWtg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CAA2C83DD27; Tue, 13 Apr 2021 08:51:15 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-128.pek2.redhat.com [10.72.13.128]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8ACD959456; Tue, 13 Apr 2021 08:51:07 +0000 (UTC) Subject: Re: [PATCH RFC v2 1/4] virtio: fix up virtio_disable_cb To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Jakub Kicinski , Wei Wang , David Miller , netdev@vger.kernel.org, Willem de Bruijn , virtualization@lists.linux-foundation.org References: <20210413054733.36363-1-mst@redhat.com> <20210413054733.36363-2-mst@redhat.com> From: Jason Wang Message-ID: <6d0666bb-7f0d-c442-13cc-9e5b715290e6@redhat.com> Date: Tue, 13 Apr 2021 16:51:05 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <20210413054733.36363-2-mst@redhat.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2021/4/13 ÏÂÎç1:47, Michael S. Tsirkin дµÀ: > virtio_disable_cb is currently a nop for split ring with event index. > This is because it used to be always called from a callback when we know > device won't trigger more events until we update the index. However, > now that we run with interrupts enabled a lot we also poll without a > callback so that is different: disabling callbacks will help reduce the > number of spurious interrupts. > Further, if using event index with a packed ring, and if being called > from a callback, we actually do disable interrupts which is unnecessary. > > Fix both issues by tracking whenever we get a callback. If that is > the case disabling interrupts with event index can be a nop. > If not the case disable interrupts. Note: with a split ring > there's no explicit "no interrupts" value. For now we write > a fixed value so our chance of triggering an interupt > is 1/ring size. It's probably better to write something > related to the last used index there to reduce the chance > even further. For now I'm keeping it simple. So I wonder whether last_used_idx is better, it looks to me the device will never move used index "across" that: https://lore.kernel.org/patchwork/patch/946475/ And it looks to me it's better to move the optimization (event_triggered) into a separated patch. > > Signed-off-by: Michael S. Tsirkin > --- > drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- > 1 file changed, 25 insertions(+), 1 deletion(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 71e16b53e9c1..88f0b16b11b8 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -113,6 +113,9 @@ struct vring_virtqueue { > /* Last used index we've seen. */ > u16 last_used_idx; > > + /* Hint for event idx: already triggered no need to disable. */ > + bool event_triggered; > + > union { > /* Available for split ring */ > struct { > @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) > > if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > - if (!vq->event) > + if (vq->event) > + /* TODO: this is a hack. Figure out a cleaner value to write. */ > + vring_used_event(&vq->split.vring) = 0x0; > + else > vq->split.vring.avail->flags = > cpu_to_virtio16(_vq->vdev, > vq->split.avail_flags_shadow); > @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > vq->weak_barriers = weak_barriers; > vq->broken = false; > vq->last_used_idx = 0; > + vq->event_triggered = false; > vq->num_added = 0; > vq->packed_ring = true; > vq->use_dma_api = vring_use_dma_api(vdev); > @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + /* If device triggered an event already it won't trigger one again: > + * no need to disable. > + */ > + if (vq->event_triggered) > + return; I guess we nee to check vq->event as well. Thanks > + > if (vq->packed_ring) > virtqueue_disable_cb_packed(_vq); > else > @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + if (vq->event_triggered) > + vq->event_triggered = false; > + > return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) : > virtqueue_enable_cb_prepare_split(_vq); > } > @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + if (vq->event_triggered) > + vq->event_triggered = false; > + > return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) : > virtqueue_enable_cb_delayed_split(_vq); > } > @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) > if (unlikely(vq->broken)) > return IRQ_HANDLED; > > + /* Just a hint for performance: so it's ok that this can be racy! */ > + if (vq->event) > + vq->event_triggered = true; > + > pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); > if (vq->vq.callback) > vq->vq.callback(&vq->vq); > @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > vq->weak_barriers = weak_barriers; > vq->broken = false; > vq->last_used_idx = 0; > + vq->event_triggered = false; > vq->num_added = 0; > vq->use_dma_api = vring_use_dma_api(vdev); > #ifdef DEBUG