From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Jakub Kicinski <kuba@kernel.org>,
Jason Wang <jasowang@redhat.com>, Wei Wang <weiwan@google.com>,
David Miller <davem@davemloft.net>,
netdev@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
virtualization@lists.linux-foundation.org
Subject: [PATCH RFC v2 1/4] virtio: fix up virtio_disable_cb
Date: Tue, 13 Apr 2021 01:47:47 -0400 [thread overview]
Message-ID: <20210413054733.36363-2-mst@redhat.com> (raw)
In-Reply-To: <20210413054733.36363-1-mst@redhat.com>
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 <mst@redhat.com>
---
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
next prev parent reply other threads:[~2021-04-13 5:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 5:47 [PATCH RFC v2 0/4] virtio net: spurious interrupt related fixes Michael S. Tsirkin
2021-04-13 5:47 ` Michael S. Tsirkin [this message]
2021-04-13 8:51 ` [PATCH RFC v2 1/4] virtio: fix up virtio_disable_cb Jason Wang
2021-04-13 14:01 ` Willem de Bruijn
2021-04-13 19:53 ` Michael S. Tsirkin
2021-04-13 21:44 ` Willem de Bruijn
2021-04-13 22:11 ` Michael S. Tsirkin
2021-04-14 0:24 ` Willem de Bruijn
2021-04-13 5:47 ` [PATCH RFC v2 2/4] virtio_net: disable cb aggressively Michael S. Tsirkin
2021-04-13 8:53 ` Jason Wang
2021-04-13 14:08 ` Willem de Bruijn
2021-04-13 14:33 ` Michael S. Tsirkin
2021-04-13 5:47 ` [PATCH RFC v2 3/4] virtio_net: move tx vq operation under tx queue lock Michael S. Tsirkin
2021-04-13 8:54 ` Jason Wang
2021-04-13 14:02 ` Michael S. Tsirkin
2021-04-13 14:20 ` Willem de Bruijn
2021-04-13 19:38 ` Michael S. Tsirkin
2021-04-13 5:47 ` [PATCH RFC v2 4/4] virtio_net: move txq wakeups under tx q lock Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210413054733.36363-2-mst@redhat.com \
--to=mst@redhat.com \
--cc=davem@davemloft.net \
--cc=jasowang@redhat.com \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=virtualization@lists.linux-foundation.org \
--cc=weiwan@google.com \
--cc=willemb@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).