From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: pagupta@redhat.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH RFC v5 net-next 2/6] virtio_ring: try to disable event index callbacks in virtqueue_disable_cb()
Date: Tue, 10 Feb 2015 11:24:17 +0100 [thread overview]
Message-ID: <20150210102417.GB9505@redhat.com> (raw)
In-Reply-To: <1423471165-34243-3-git-send-email-jasowang@redhat.com>
On Mon, Feb 09, 2015 at 03:39:21AM -0500, Jason Wang wrote:
> Currently, we do nothing to prevent the callbacks in
> virtqueue_disable_cb() when event index is used. This may cause
> spurious interrupts which may damage the performance. This patch tries
> to publish avail event as the used even to prevent the callbacks.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
I'm surprised that this ever happens though.
Normally we call this after getting an interrupt, and
interrupts won't trigger again until the rings wraps around.
When I tested this, touching an extra cache line was more
expensive.
Does this really reduce number of interrupts?
Could you pls share some numbers with and without this patch?
> ---
> drivers/virtio/virtio_ring.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 545fed5..e9ffbfb 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -539,6 +539,8 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
> struct vring_virtqueue *vq = to_vvq(_vq);
>
> vq->vring.avail->flags |= cpu_to_virtio16(_vq->vdev, VRING_AVAIL_F_NO_INTERRUPT);
> + vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
> + vq->vring.avail->idx);
Hmm in fact, can't this actually cause an extra interrupt
when avail->idx is completed?
I think that if you really can show disabling interrupts like this helps, you should
set some invalid value like 0xfffff, or move it back to vq->vring.avail->idx - 1.
No?
> }
> EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
>
> --
> 1.8.3.1
next prev parent reply other threads:[~2015-02-10 10:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-09 8:39 [PATCH RFC v5 net-next 0/6] enable tx interrupts for virtio-net Jason Wang
2015-02-09 8:39 ` [PATCH RFC v5 net-next 1/6] virtio_ring: fix virtqueue_enable_cb() when only 1 buffers were pending Jason Wang
2015-02-10 1:03 ` Rusty Russell
2015-02-10 6:26 ` Jason Wang
2015-02-10 10:18 ` Michael S. Tsirkin
2015-02-10 23:58 ` Rusty Russell
2015-02-11 5:41 ` Jason Wang
2015-02-09 8:39 ` [PATCH RFC v5 net-next 2/6] virtio_ring: try to disable event index callbacks in virtqueue_disable_cb() Jason Wang
2015-02-10 1:07 ` Rusty Russell
2015-02-10 10:24 ` Michael S. Tsirkin [this message]
2015-02-11 5:55 ` Jason Wang
2015-02-09 8:39 ` [PATCH RFC v5 net-next 3/6] virtio_net: enable tx interrupt Jason Wang
2015-02-09 8:39 ` [PATCH RFC v5 net-next 4/6] virtio-net: add basic interrupt coalescing support Jason Wang
2015-02-10 1:32 ` Rusty Russell
2015-02-10 6:51 ` Jason Wang
2015-02-10 10:25 ` Michael S. Tsirkin
2015-02-10 10:40 ` Michael S. Tsirkin
2015-02-13 2:52 ` Rusty Russell
2015-02-13 12:41 ` Pawel Moll
2015-02-16 3:07 ` Rusty Russell
2015-02-13 18:19 ` Cornelia Huck
2015-02-16 3:19 ` Rusty Russell
2015-02-09 8:39 ` [PATCH RFC v5 net-next 5/6] vhost: let vhost_signal() returns whether signalled Jason Wang
2015-02-09 8:39 ` [PATCH RFC v5 net-next 6/6] vhost_net: interrupt coalescing support Jason Wang
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=20150210102417.GB9505@redhat.com \
--to=mst@redhat.com \
--cc=jasowang@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=pagupta@redhat.com \
--cc=virtualization@lists.linux-foundation.org \
/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).