From: "Fu, Patrick" <patrick.fu@intel.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Xia, Chenbo" <chenbo.xia@intel.com>
Subject: Re: [dpdk-dev] [PATCH v1] vhost: support cross page buf in async data path
Date: Tue, 21 Jul 2020 02:57:36 +0000 [thread overview]
Message-ID: <BYAPR11MB37355A9E0699BD06D75E2E3284780@BYAPR11MB3735.namprd11.prod.outlook.com> (raw)
In-Reply-To: <b9c25966-f934-e416-0c0a-4693929d37cd@redhat.com>
Hi Maxime,
> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Tuesday, July 21, 2020 12:40 AM
> To: Fu, Patrick <patrick.fu@intel.com>; dev@dpdk.org; Xia, Chenbo
> <chenbo.xia@intel.com>
> Subject: Re: [PATCH v1] vhost: support cross page buf in async data path
>
> The title could be improved, it is not very clear IMHO.
How about:
vhost: fix async copy failure on buffers cross page boundary
> On 7/20/20 4:52 AM, patrick.fu@intel.com wrote:
> > From: Patrick Fu <patrick.fu@intel.com>
> >
> > Async copy fails when ring buffer cross two physical pages. This patch
> > fix the failure by letting copies occur in sync mode if crossing page
> > buffers are given.
>
> Wouldn't it be possible to have the buffer split into two iovecs?
Technically we can do that, however, it will also introduce significant overhead:
- overhead from adding additional logic in vhost async data path to handle the case
- overhead from dma device to consume 2 iovecs
In average, I don't think dma copy can benefit too much for the buffer which are split into multiple pages.
CPU copy shall be a more suitable method.
> > Fixes: cd6760da1076 ("vhost: introduce async enqueue for split ring")
> >
> > Signed-off-by: Patrick Fu <patrick.fu@intel.com>
> > ---
> > lib/librte_vhost/virtio_net.c | 12 +++---------
> > 1 file changed, 3 insertions(+), 9 deletions(-)
> >
> > diff --git a/lib/librte_vhost/virtio_net.c
> > b/lib/librte_vhost/virtio_net.c index 1d0be3dd4..44b22a8ad 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -1071,16 +1071,10 @@ async_mbuf_to_desc(struct virtio_net *dev,
> struct vhost_virtqueue *vq,
> > }
> >
> > cpy_len = RTE_MIN(buf_avail, mbuf_avail);
> > + hpa = (void *)(uintptr_t)gpa_to_hpa(dev,
> > + buf_iova + buf_offset, cpy_len);
> >
> > - if (unlikely(cpy_len >= cpy_threshold)) {
> > - hpa = (void *)(uintptr_t)gpa_to_hpa(dev,
> > - buf_iova + buf_offset, cpy_len);
> > -
> > - if (unlikely(!hpa)) {
> > - error = -1;
> > - goto out;
> > - }
> > -
> > + if (unlikely(cpy_len >= cpy_threshold && hpa)) {
> > async_fill_vec(src_iovec + tvec_idx,
> > (void *)(uintptr_t)rte_pktmbuf_iova_offset(m,
> > mbuf_offset), cpy_len);
> >
next prev parent reply other threads:[~2020-07-21 2:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-20 2:52 patrick.fu
2020-07-20 16:39 ` Maxime Coquelin
2020-07-21 2:57 ` Fu, Patrick [this message]
2020-07-21 8:35 ` Maxime Coquelin
2020-07-21 9:01 ` Fu, Patrick
2020-07-24 13:49 ` [dpdk-dev] [PATCH v2] vhost: fix async copy fail on multi-page buffers patrick.fu
2020-07-27 6:33 ` [dpdk-dev] [PATCH v3] " patrick.fu
2020-07-27 13:14 ` Xia, Chenbo
2020-07-28 3:09 ` Fu, Patrick
2020-07-28 3:28 ` [dpdk-dev] [PATCH v4] " patrick.fu
2020-07-28 13:55 ` Maxime Coquelin
2020-07-29 1:40 ` Fu, Patrick
2020-07-29 2:05 ` Fu, Patrick
2020-07-29 2:04 ` [dpdk-dev] [PATCH v5] " Patrick Fu
2020-07-29 14:24 ` Maxime Coquelin
2020-07-29 14:55 ` Maxime Coquelin
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