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Tsirkin" , Jason Wang , Sasha Levin Subject: [PATCH 6.1 454/611] virtio_ring: dont update event idx on get_buf Date: Mon, 8 May 2023 11:44:56 +0200 Message-Id: <20230508094436.910775778@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230508094421.513073170@linuxfoundation.org> References: <20230508094421.513073170@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Albert Huang [ Upstream commit 6c0b057cec5eade4c3afec3908821176931a9997 ] In virtio_net, if we disable napi_tx, when we trigger a tx interrupt, the vq->event_triggered will be set to true. It is then never reset until we explicitly call virtqueue_enable_cb_delayed or virtqueue_enable_cb_prepare. If we disable the napi_tx, virtqueue_enable_cb* will only be called when the tx ring is getting relatively empty. Since event_triggered is true, VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE will not be set. As a result we update vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap every time we call virtqueue_get_buf_ctx. This causes more interrupts. To summarize: 1) event_triggered was set to true in vring_interrupt() 2) after this nothing will happen in virtqueue_disable_cb() so VRING_AVAIL_F_NO_INTERRUPT is not set in avail_flags_shadow 3) virtqueue_get_buf_ctx_split() will still think the cb is enabled and then it will publish a new event index To fix: update VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE in the vq when we call virtqueue_disable_cb even when event_triggered is true. Tested with iperf: iperf3 tcp stream: vm1 -----------------> vm2 vm2 just receives tcp data stream from vm1, and sends acks to vm1, there are many tx interrupts in vm2. with the patch applied there are just a few tx interrupts. v2->v3: -update the interrupt disable flag even with the event_triggered is set, -instead of checking whether event_triggered is set in -virtqueue_get_buf_ctx_{packed/split}, will cause the drivers which have -not called virtqueue_{enable/disable}_cb to miss notifications. v3->v4: -remove change for -"if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE)" -in virtqueue_disable_cb_packed Fixes: 8d622d21d248 ("virtio: fix up virtio_disable_cb") Signed-off-by: Albert Huang Signed-off-by: Michael S. Tsirkin Signed-off-by: Jason Wang Message-Id: <20230329102300.61000-1-huangjie.albert@bytedance.com> Signed-off-by: Michael S. Tsirkin Signed-off-by: Sasha Levin --- drivers/virtio/virtio_ring.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 2e7689bb933b8..90d514c141794 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -848,6 +848,14 @@ 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 device triggered an event already it won't trigger one again: + * no need to disable. + */ + if (vq->event_triggered) + return; + if (vq->event) /* TODO: this is a hack. Figure out a cleaner value to write. */ vring_used_event(&vq->split.vring) = 0x0; @@ -1687,6 +1695,14 @@ static void virtqueue_disable_cb_packed(struct virtqueue *_vq) if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE) { vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE; + + /* + * If device triggered an event already it won't trigger one again: + * no need to disable. + */ + if (vq->event_triggered) + return; + vq->packed.vring.driver->flags = cpu_to_le16(vq->packed.event_flags_shadow); } @@ -2309,12 +2325,6 @@ 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 -- 2.39.2