[v1] vhost: support cross page buf in async data path
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Commit Message
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.
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(-)
Comments
The title could be improved, it is not very clear IMHO.
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?
> 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);
>
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);
> >
Hi Patrick,
On 7/21/20 4:57 AM, Fu, Patrick wrote:
> 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.
I think we should try, that would make a cleaner implementation. I don't
think having to fallback to sync mode is a good idea because it adds an
overhead on the CPU, which is what we try to avoid with this async mode.
Also, I am not convinced the overhead would be that significant, at
least I hope so, otherwise it would mean this new path is just
performing better because it takes a lot of shortcuts, like the vector
path in Virtio PMD.
Regards,
Maxime
>
>>> 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);
>>>
>
Hi Maxime,
> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Tuesday, July 21, 2020 4:35 PM
> 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
>
> Hi Patrick,
>
> On 7/21/20 4:57 AM, Fu, Patrick wrote:
> > 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.
>
> I think we should try, that would make a cleaner implementation. I don't
> think having to fallback to sync mode is a good idea because it adds an
> overhead on the CPU, which is what we try to avoid with this async mode.
>
> Also, I am not convinced the overhead would be that significant, at least I
> hope so, otherwise it would mean this new path is just performing better
> because it takes a lot of shortcuts, like the vector path in Virtio PMD.
I can make a trial patch and do some comparison. I will try to feedback the result by this weekend.
Thanks,
Patrick
@@ -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);