LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Jason Wang <jasowang@redhat.com>
To: Tiwei Bie <tiwei.bie@intel.com>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
wexu@redhat.com, jfreimann@redhat.com
Subject: Re: [RFC v3 4/5] virtio_ring: add event idx support in packed ring
Date: Thu, 3 May 2018 15:25:29 +0800 [thread overview]
Message-ID: <9f0b4e37-63ff-42f9-f2e6-3747a19a0206@redhat.com> (raw)
In-Reply-To: <20180503020949.5u3qz32gsk33z6vk@debian>
On 2018年05月03日 10:09, Tiwei Bie wrote:
>>>> So how about we use the straightforward way then?
>>> You mean we do new += vq->vring_packed.num instead
>>> of event_idx -= vq->vring_packed.num before calling
>>> vring_need_event()?
>>>
>>> The problem is that, the second param (new_idx) of
>>> vring_need_event() will be used for:
>>>
>>> (__u16)(new_idx - event_idx - 1)
>>> (__u16)(new_idx - old)
>>>
>>> So if we change new, we will need to change old too.
>> I think that since we have a branch there anyway,
>> we are better off just special-casing if (wrap_counter != vq->wrap_counter).
>> Treat is differenty and avoid casts.
>>
>>> And that would be an ugly hack..
>>>
>>> Best regards,
>>> Tiwei Bie
>> I consider casts and huge numbers with two's complement
>> games even uglier.
> The dependency on two's complement game is introduced
> since the split ring.
>
> In packed ring, old is calculated via:
>
> old = vq->next_avail_idx - vq->num_added;
>
> In split ring, old is calculated via:
>
> old = vq->avail_idx_shadow - vq->num_added;
>
> In both cases, when vq->num_added is bigger, old will
> be a big number.
>
> Best regards,
> Tiwei Bie
>
How about just do something like vhost:
static u16 vhost_idx_diff(struct vhost_virtqueue *vq, u16 old, u16 new)
{
if (new > old)
return new - old;
return (new + vq->num - old);
}
static bool vhost_vring_packed_need_event(struct vhost_virtqueue *vq,
__u16 event_off, __u16 new,
__u16 old)
{
return (__u16)(vhost_idx_diff(vq, new, event_off) - 1) <
(__u16)vhost_idx_diff(vq, new, old);
}
?
next prev parent reply other threads:[~2018-05-03 7:25 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-25 5:15 [RFC v3 0/5] virtio: support " Tiwei Bie
2018-04-25 5:15 ` [RFC v3 1/5] virtio: add packed ring definitions Tiwei Bie
2018-04-25 5:15 ` [RFC v3 2/5] virtio_ring: support creating packed ring Tiwei Bie
2018-04-25 5:15 ` [RFC v3 3/5] virtio_ring: add packed ring support Tiwei Bie
2018-05-10 7:32 ` Jason Wang
2018-05-10 7:34 ` Jason Wang
2018-05-10 8:56 ` Tiwei Bie
2018-05-10 9:49 ` Jason Wang
2018-05-10 10:50 ` Tiwei Bie
2018-04-25 5:15 ` [RFC v3 4/5] virtio_ring: add event idx support in packed ring Tiwei Bie
2018-05-02 2:51 ` Jason Wang
2018-05-02 7:28 ` Tiwei Bie
2018-05-02 13:51 ` Michael S. Tsirkin
2018-05-02 15:12 ` Tiwei Bie
2018-05-02 15:42 ` Michael S. Tsirkin
2018-05-03 1:11 ` Tiwei Bie
2018-05-03 1:44 ` Michael S. Tsirkin
2018-05-03 2:09 ` Tiwei Bie
2018-05-03 7:25 ` Jason Wang [this message]
2018-05-03 13:54 ` Tiwei Bie
2018-05-08 3:05 ` Jason Wang
2018-05-08 5:40 ` Jason Wang
2018-05-08 6:44 ` Tiwei Bie
2018-05-08 7:16 ` Jason Wang
2018-05-08 9:16 ` Tiwei Bie
2018-05-08 9:34 ` Jason Wang
2018-05-08 9:44 ` Tiwei Bie
2018-05-09 3:43 ` Jason Wang
2018-05-16 5:01 ` Jason Wang
2018-05-16 5:55 ` Tiwei Bie
2018-04-25 5:15 ` [RFC v3 5/5] virtio_ring: enable " Tiwei Bie
2018-04-27 3:56 ` [RFC v3 0/5] virtio: support " Jason Wang
2018-04-27 4:18 ` Michael S. Tsirkin
2018-04-27 6:17 ` Jason Wang
2018-04-27 9:12 ` Tiwei Bie
2018-04-28 2:45 ` Jason Wang
2018-05-02 3:49 ` 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=9f0b4e37-63ff-42f9-f2e6-3747a19a0206@redhat.com \
--to=jasowang@redhat.com \
--cc=jfreimann@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=tiwei.bie@intel.com \
--cc=virtualization@lists.linux-foundation.org \
--cc=wexu@redhat.com \
--subject='Re: [RFC v3 4/5] virtio_ring: add event idx support in packed ring' \
/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
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).