From: Eugenio Perez Martin <eperezma@redhat.com>
To: Kevin Traynor <ktraynor@redhat.com>,
Maxime Coquelin <mcoqueli@redhat.com>
Cc: dev@dpdk.org, "Liu, Yong" <yong.liu@intel.com>,
Adrian Moreno Zapata <amorenoz@redhat.com>,
Jason Wang <jasowang@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [dpdk-dev] [PATCH] vhost: flush shadow tx if there is no more packets
Date: Tue, 4 Feb 2020 16:05:46 +0100 [thread overview]
Message-ID: <CAJaqyWfMUk4h=EvYp_BHUdOHYn_u4VTcHLLhRsWZ2A1e1t8cnA@mail.gmail.com> (raw)
In-Reply-To: <edaf7ef4-621e-69ed-57d7-e9838990a238@redhat.com>
Ouch, my bad again, sorry :).
I've forwarded the patch to stable@, please let me know if I need to do
something else.
Maxime, please let me know if I need to send a new version with the "Fixed:
" tag :).
Thanks!
On Tue, Feb 4, 2020 at 2:49 PM Kevin Traynor <ktraynor@redhat.com> wrote:
> On 04/02/2020 09:23, Eugenio Perez Martin wrote:
> > Hi Kevin!
> >
> > Sorry, thanks for noticing it! It fixes commit ("31d6c6a5b vhost:
> optimize
> > packed ring dequeue"), what was not present on 18.11 version (I've
> checked
> > that v19.08 does not contain the failure).
> >
>
> Right, in that case the issue is present on 19.11 stable, so it's worth
> adding the tags to get it fixed in 19.11 stable.
>
> > Do I need to send another patch version with corrected commit message?
> >
>
> Probably Maxime can do it on applying if you ask nicely :-)
>
> > Thanks!
> >
> > On Fri, Jan 31, 2020 at 7:38 PM Kevin Traynor <ktraynor@redhat.com>
> wrote:
> >
> >> Hi Eugenio,
> >>
> >> On 29/01/2020 19:33, Eugenio Pérez wrote:
> >>> The current implementation of vhost_net in packed vring tries to fill
> >>> the shadow vector before send any actual changes to the guest. While
> >>> this can be beneficial for the throughput, it conflicts with some
> >>> bufferfloats methods like the linux kernel napi, that stops
> >>> transmitting packets if there are too much bytes/buffers in the
> >>> driver.
> >>>
> >>> To solve it, we flush the shadow packets at the end of
> >>> virtio_dev_tx_packed if we have starved the vring, i.e., the next
> >>> buffer is not available for the device.
> >>>
> >>> Since this last check can be expensive because of the atomic, we only
> >>> check it if we have not obtained the expected (count) packets. If it
> >>> happens to obtain "count" packets and there is no more available
> >>> packets the caller needs to keep call virtio_dev_tx_packed again.
> >>>
> >>
> >> It seems to be fixing an issue and should be considered for stable
> >> branches? You can add the tags needed in the commit message here:
> >>
> >> Fixes: <commit that introduced bug/missed this case>
> >> Cc: stable@dpdk.org
> >>
> >>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> >>> ---
> >>> lib/librte_vhost/virtio_net.c | 27 ++++++++++++++++++++++++++-
> >>> 1 file changed, 26 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/lib/librte_vhost/virtio_net.c
> >> b/lib/librte_vhost/virtio_net.c
> >>> index 21c311732..ac2842b2d 100644
> >>> --- a/lib/librte_vhost/virtio_net.c
> >>> +++ b/lib/librte_vhost/virtio_net.c
> >>> @@ -2133,6 +2133,20 @@ virtio_dev_tx_packed_zmbuf(struct virtio_net
> *dev,
> >>> return pkt_idx;
> >>> }
> >>>
> >>> +static __rte_always_inline bool
> >>> +next_desc_is_avail(const struct vhost_virtqueue *vq)
> >>> +{
> >>> + bool wrap_counter = vq->avail_wrap_counter;
> >>> + uint16_t next_used_idx = vq->last_used_idx + 1;
> >>> +
> >>> + if (next_used_idx >= vq->size) {
> >>> + next_used_idx -= vq->size;
> >>> + wrap_counter ^= 1;
> >>> + }
> >>> +
> >>> + return desc_is_avail(&vq->desc_packed[next_used_idx],
> >> wrap_counter);
> >>> +}
> >>> +
> >>> static __rte_noinline uint16_t
> >>> virtio_dev_tx_packed(struct virtio_net *dev,
> >>> struct vhost_virtqueue *vq,
> >>> @@ -2165,9 +2179,20 @@ virtio_dev_tx_packed(struct virtio_net *dev,
> >>>
> >>> } while (remained);
> >>>
> >>> - if (vq->shadow_used_idx)
> >>> + if (vq->shadow_used_idx) {
> >>> do_data_copy_dequeue(vq);
> >>>
> >>> + if (remained && !next_desc_is_avail(vq)) {
> >>> + /*
> >>> + * The guest may be waiting to TX some buffers to
> >>> + * enqueue more to avoid bufferfloat, so we try
> to
> >>> + * reduce latency here.
> >>> + */
> >>> + vhost_flush_dequeue_shadow_packed(dev, vq);
> >>> + vhost_vring_call_packed(dev, vq);
> >>> + }
> >>> + }
> >>> +
> >>> return pkt_idx;
> >>> }
> >>>
> >>>
> >>
> >>
> >
>
>
next prev parent reply other threads:[~2020-02-04 15:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 15:47 [dpdk-dev] [Bug 383] dpdk virtio_user lack of notifications make vhost_net+napi stops tx buffers bugzilla
2020-01-09 15:55 ` eperezma
2020-01-15 7:05 ` Liu, Yong
2020-01-29 19:33 ` [dpdk-dev] [PATCH] vhost: flush shadow tx if there is no more packets Eugenio Pérez
2020-01-31 18:38 ` Kevin Traynor
2020-02-04 9:23 ` Eugenio Perez Martin
2020-02-04 13:48 ` Kevin Traynor
2020-02-04 15:05 ` Eugenio Perez Martin [this message]
2020-02-04 15:10 ` Maxime Coquelin
2020-02-05 9:09 ` Maxime Coquelin
2020-02-05 9:47 ` Maxime Coquelin
2020-02-05 15:45 ` Eugenio Perez Martin
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