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=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,USER_AGENT_GIT 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 B014AC07E9E for ; Sat, 10 Jul 2021 23:52:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E545613FC for ; Sat, 10 Jul 2021 23:52:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233538AbhGJXyx (ORCPT ); Sat, 10 Jul 2021 19:54:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:41376 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233545AbhGJXx5 (ORCPT ); Sat, 10 Jul 2021 19:53:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 65C49613E7; Sat, 10 Jul 2021 23:51:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1625961066; bh=EqY3s3uZCH/3kT+7Qix6kDh4PwexwXrGB3dJQFtlQJc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=louU74yTxJYCSf5hOOIHTs3wUa6b9ymSoCcP3d4KVglw37yM+avGUeFV2Iul+8w3M BKz0r1ngvEbMJmmKlTJMxLBsLMsN0EkBPG3dHyr9eUur+u54WD3QjShF0WUh4EOGpv hqm/4LwlCvVIgEMjpSLR5y535T+fwwGoKXwAXSG/eXSPsnSmFsY69QglplCd0K4hxC FqcQYR8hRGJPfJiJSpKIpBz0rl3s0N9RgI7KWKtF8VsFsAbbwpRurAS0FN7hd+bVBt aAe7aCkDtlmlkbRf186IvWRKPDjeFij4nGvNeuOhPaw+Nu3T/PzXbK1y5VLmgxkoWl ue4Q+LQWuWe4A== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "Michael S. Tsirkin" , Sasha Levin , virtualization@lists.linux-foundation.org Subject: [PATCH AUTOSEL 5.10 37/37] virtio: fix up virtio_disable_cb Date: Sat, 10 Jul 2021 19:50:15 -0400 Message-Id: <20210710235016.3221124-37-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210710235016.3221124-1-sashal@kernel.org> References: <20210710235016.3221124-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Michael S. Tsirkin" [ Upstream commit 8d622d21d24803408b256d96463eac4574dcf067 ] 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. Signed-off-by: Michael S. Tsirkin Signed-off-by: Sasha Levin --- 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 -- 2.30.2