Re: [dpdk-dev] [PATCH 1/4] vhost: inroduce operation to get vDPA queue stats

[Shahaf Shuler <shahafs@mellanox.com>]

Monday, April 20, 2020 7:19 PM, Maxime Coquelin:
> Cc: Slava Ovsiienko <viacheslavo@mellanox.com>
> Subject: Re: [PATCH 1/4] vhost: inroduce operation to get vDPA queue stats
> 
> 
> 
> On 4/20/20 5:57 PM, Shahaf Shuler wrote:
> > Monday, April 20, 2020 10:13 AM, Maxime Coquelin:
> >> Subject: Re: [PATCH 1/4] vhost: inroduce operation to get vDPA queue
> >> stats
> >>
> >> Hi Shahaf,
> >>
> >> On 4/19/20 8:18 AM, Shahaf Shuler wrote:
> >>> Thursday, April 16, 2020 4:20 PM, Maxime Coquelin:
> >>>> Subject: Re: [PATCH 1/4] vhost: inroduce operation to get vDPA
> >>>> queue stats
> >>>>
> >>>> Hi Matan,
> >>>>
> >>>> On 4/16/20 11:06 AM, Matan Azrad wrote:
> >>>>> Hi Maxime
> >>>>>
> >>>>> Can you point on specific vendor specific counter I suggested?
> >>>>
> >>>> No, I can't, but I think we can expect that other vendors may have
> >>>> other counters they would be interested to dump.
> >>>>
> >>>> Maybe Intel has some counters in the IFC that they could dump.
> >>>> Xiao, any thoughts?
> >>>>
> >>>>> I think all of them come directly from virtio protocols.
> >>>>
> >>>> exceed_max_chain, for example. Doesn't the spec specify that a
> >>>> descriptors chain can be as long as the size of the virtqueue?
> >>>>
> >>>> Here it seems to indicate the device could support less.
> >>>
> >>> Spec allows device to limit the max supported chain (see [1]).
> >>
> >> Ha ok, I missed that. Please note that this is only allowed for
> >> packed ring, it is not in the split ring part.
> >
> > On my version of spec (csprd01) it is also for split, however it was removed
> on the latest version not sure why.

Actually also for split queue there is this vouge paragraph -
https://github.com/oasis-tcs/virtio-spec/blob/master/split-ring.tex#L138

> 
> Problem is that older drivers may assume max chain size is the virtio ring size.
> 
> By the way, how is the guest Virtio driver made aware of the max chain size?
> Isn't that missing in the spec?

Spec gap. Doesn't say how device report, doesn’t device how device should fail and report error. 

>