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Tsirkin " , Jason Wang Cc: "huangjie.albert" , virtualization@lists.linux-foundation.org (open list:VIRTIO CORE AND NET DRIVERS), linux-kernel@vger.kernel.org (open list) Subject: [PATCH] virtio_ring: Suppress tx interrupt when napi_tx disable Date: Tue, 21 Mar 2023 16:59:53 +0800 Message-Id: <20230321085953.24949-1-huangjie.albert@bytedance.com> X-Mailer: git-send-email 2.37.0 (Apple Git-136) MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1760969842062319270?= X-GMAIL-MSGID: =?utf-8?q?1760969842062319270?= From: "huangjie.albert" fix commit 8d622d21d248 ("virtio: fix up virtio_disable_cb") if we disable the napi_tx. when we triger a tx interrupt, the vq->event_triggered will be set to true. It will no longer be set to false. Unless we explicitly call virtqueue_enable_cb_delayed or virtqueue_enable_cb_prepare if we disable the napi_tx, It will only be called when the tx ring buffer is relatively small: virtio_net->start_xmit: if (sq->vq->num_free < 2+MAX_SKB_FRAGS) { netif_stop_subqueue(dev, qnum); if (!use_napi && unlikely(!virtqueue_enable_cb_delayed(sq->vq))) { /* More just got used, free them then recheck. */ free_old_xmit_skbs(sq, false); if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) { netif_start_subqueue(dev, qnum); virtqueue_disable_cb(sq->vq); } } } Because event_triggered is true.Therefore, VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE will not be set.So we update vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap every time we call virtqueue_get_buf_ctx.This will bring more interruptions. if event_triggered is set to true, do not update vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap Signed-off-by: huangjie.albert --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 307e139cb11d..f486cccadbeb 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -795,7 +795,8 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, /* If we expect an interrupt for the next entry, tell host * by writing event index and flush out the write before * the read in the next get_buf call. */ - if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) + if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) + && (vq->event_triggered == false)) virtio_store_mb(vq->weak_barriers, &vring_used_event(&vq->split.vring), cpu_to_virtio16(_vq->vdev, vq->last_used_idx)); @@ -1529,7 +1530,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, * by writing event index and flush out the write before * the read in the next get_buf call. */ - if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC) + if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC + && (vq->event_triggered == false)) virtio_store_mb(vq->weak_barriers, &vq->packed.vring.driver->off_wrap, cpu_to_le16(vq->last_used_idx));