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 93180C74A5B for ; Thu, 30 Mar 2023 06:59:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230395AbjC3G7w (ORCPT ); Thu, 30 Mar 2023 02:59:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229914AbjC3G7q (ORCPT ); Thu, 30 Mar 2023 02:59:46 -0400 Received: from out30-118.freemail.mail.aliyun.com (out30-118.freemail.mail.aliyun.com [115.124.30.118]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 883B16A40; Wed, 29 Mar 2023 23:59:37 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R351e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=xuanzhuo@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0VezVY5m_1680159573; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0VezVY5m_1680159573) by smtp.aliyun-inc.com; Thu, 30 Mar 2023 14:59:34 +0800 Message-ID: <1680159261.1588428-1-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH v3 3/4] virtio: fix up virtio_disable_cb Date: Thu, 30 Mar 2023 14:54:21 +0800 From: Xuan Zhuo To: "Michael S. Tsirkin" Cc: Willem de Bruijn , netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, Jakub Kicinski , Wei Wang , David Miller , linux-kernel@vger.kernel.org References: <20210526082423.47837-1-mst@redhat.com> <20210526082423.47837-4-mst@redhat.com> <1680156457.5551112-5-xuanzhuo@linux.alibaba.com> <20230330024220-mutt-send-email-mst@kernel.org> In-Reply-To: <20230330024220-mutt-send-email-mst@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 30 Mar 2023 02:44:44 -0400, "Michael S. Tsirkin" wrote: > On Thu, Mar 30, 2023 at 02:07:37PM +0800, Xuan Zhuo wrote: > > On Wed, 26 May 2021 04:24:40 -0400, "Michael S. Tsirkin" wrote: > > > 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. > > > > > > Don't understand, is this patch necessary? For this patch set, we can do without > > this patch. > > > > So doest this patch optimize virtqueue_disable_cb() by reducing a modification of > > vring_used_event(&vq-> split.vring)? > > > > Or I miss something. > > > > Thanks. > > Before this patch virtqueue_disable_cb did nothing at all > for the common case of event index enabled, so > calling it from virtio net would not help matters. I agree with these codes: - 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 I just don't understand event_triggered. > > But the patch is from 2021, isn't it a bit too late to argue? > If you have a cleanup or an optimization in mind, please > post a patch. Sorry, I just have some problems, I don't oppose it. At least it can reduce the modification of vring_used_event(&vq->split.vring). I think it is also beneficial. Thanks very much. > > > > > > > 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; > > > + > > > 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 > > > -- > > > MST > > > > > > _______________________________________________ > > > Virtualization mailing list > > > Virtualization@lists.linux-foundation.org > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization > 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 smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A299EC761AF for ; Thu, 30 Mar 2023 06:59:44 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 0877E41DEA; Thu, 30 Mar 2023 06:59:44 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org 0877E41DEA X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id f9dGCItPIzTc; Thu, 30 Mar 2023 06:59:43 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp2.osuosl.org (Postfix) with ESMTPS id 5318641DDD; Thu, 30 Mar 2023 06:59:42 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org 5318641DDD Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 2B047C0036; Thu, 30 Mar 2023 06:59:42 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id 06CC6C002F for ; Thu, 30 Mar 2023 06:59:41 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id C394441DE2 for ; Thu, 30 Mar 2023 06:59:40 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org C394441DE2 X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 7lYncEXhTj6t for ; Thu, 30 Mar 2023 06:59:39 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org E83D841DDD Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) by smtp2.osuosl.org (Postfix) with ESMTPS id E83D841DDD for ; Thu, 30 Mar 2023 06:59:38 +0000 (UTC) X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R351e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=ay29a033018045168; MF=xuanzhuo@linux.alibaba.com; NM=1; PH=DS; RN=8; SR=0; TI=SMTPD_---0VezVY5m_1680159573; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0VezVY5m_1680159573) by smtp.aliyun-inc.com; Thu, 30 Mar 2023 14:59:34 +0800 Message-ID: <1680159261.1588428-1-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH v3 3/4] virtio: fix up virtio_disable_cb Date: Thu, 30 Mar 2023 14:54:21 +0800 From: Xuan Zhuo To: "Michael S. Tsirkin" References: <20210526082423.47837-1-mst@redhat.com> <20210526082423.47837-4-mst@redhat.com> <1680156457.5551112-5-xuanzhuo@linux.alibaba.com> <20230330024220-mutt-send-email-mst@kernel.org> In-Reply-To: <20230330024220-mutt-send-email-mst@kernel.org> Cc: Willem de Bruijn , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Jakub Kicinski , Wei Wang , David Miller X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, 30 Mar 2023 02:44:44 -0400, "Michael S. Tsirkin" wrote: > On Thu, Mar 30, 2023 at 02:07:37PM +0800, Xuan Zhuo wrote: > > On Wed, 26 May 2021 04:24:40 -0400, "Michael S. Tsirkin" wrote: > > > 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. > > > > > > Don't understand, is this patch necessary? For this patch set, we can do without > > this patch. > > > > So doest this patch optimize virtqueue_disable_cb() by reducing a modification of > > vring_used_event(&vq-> split.vring)? > > > > Or I miss something. > > > > Thanks. > > Before this patch virtqueue_disable_cb did nothing at all > for the common case of event index enabled, so > calling it from virtio net would not help matters. I agree with these codes: - 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 I just don't understand event_triggered. > > But the patch is from 2021, isn't it a bit too late to argue? > If you have a cleanup or an optimization in mind, please > post a patch. Sorry, I just have some problems, I don't oppose it. At least it can reduce the modification of vring_used_event(&vq->split.vring). I think it is also beneficial. Thanks very much. > > > > > > > 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; > > > + > > > 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 > > > -- > > > MST > > > > > > _______________________________________________ > > > Virtualization mailing list > > > Virtualization@lists.linux-foundation.org > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization