RE: [Patch v2] net/netvsc: report correct stats values

[Long Li <longli@microsoft.com>]

> Subject: Re: [Patch v2] net/netvsc: report correct stats values
> 
> On 5/10/2022 6:33 AM, Long Li wrote:
> >> Subject: Re: [Patch v2] net/netvsc: report correct stats values
> >>
> >> On 5/5/2022 5:40 PM, Stephen Hemminger wrote:
> >>> On Thu, 5 May 2022 17:28:38 +0100
> >>> Ferruh Yigit <ferruh.yigit@xilinx.com> wrote:
> >>>
> >>>> On 5/4/2022 7:38 PM, Long Li wrote:
> >>>>>> Subject: Re: [Patch v2] net/netvsc: report correct stats values
> >>>>>>
> >>>>>> On 5/3/2022 9:48 PM, Long Li wrote:
> >>>>>>>> Subject: Re: [Patch v2] net/netvsc: report correct stats values
> >>>>>>>>
> >>>>>>>> On 5/3/2022 8:14 PM, Long Li wrote:
> >>>>>>>>>> Subject: Re: [Patch v2] net/netvsc: report correct stats
> >>>>>>>>>> values
> >>>>>>>>>>
> >>>>>>>>>> On 5/3/2022 7:18 PM, Long Li wrote:
> >>>>>>>>>>>> Subject: Re: [Patch v2] net/netvsc: report correct stats
> >>>>>>>>>>>> values
> >>>>>>>>>>>>
> >>>>>>>>>>>> On Tue, 26 Apr 2022 22:56:14 +0100 Ferruh Yigit
> >>>>>>>>>>>> <ferruh.yigit@xilinx.com> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>>>>         		if (i < RTE_ETHDEV_QUEUE_STAT_CNTRS) {
> >>>>>>>>>>>>>> -			stats->q_opackets[i] = txq-
> >stats.packets;
> >>>>>>>>>>>>>> -			stats->q_obytes[i] = txq->stats.bytes;
> >>>>>>>>>>>>>> +			stats->q_opackets[i] += txq-
> >>> stats.packets;
> >>>>>>>>>>>>>> +			stats->q_obytes[i] += txq->stats.bytes;
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> This is per queue stats, 'stats->q_opackets[i]', in next
> >>>>>>>>>>>>> iteration of the loop, 'i' will be increased and 'txq'
> >>>>>>>>>>>>> will be updated, so as far as I can see the above change has no
> affect.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Agree, that is why it was just assignment originally.
> >>>>>>>>>>>
> >>>>>>>>>>> The condition here is a little different. NETVSC is a master
> >>>>>>>>>>> device with
> >>>>>>>>>> another PMD running as a slave. When reporting stats values,
> >>>>>>>>>> it needs to add the values from the slave PMD. The original
> >>>>>>>>>> code just overwrites the values from its slave PMD.
> >>>>>>>>>>
> >>>>>>>>>> Where the initial values are coming from, 'hn_vf_stats_get()'?
> >>>>>>>>>>
> >>>>>>>>>> If 'hn_vf_stats_get()' fills the stats, what are the values
> >>>>>>>>>> kept in
> >>>>>>>>>> 'txq-
> >>>>>>>>> stats.*'
> >>>>>>>>>> in above updated loop?
> >>>>>>>>>
> >>>>>>>>> Yes, hn_vf_stats_get() fills in the stats from the slave PMD.
> >>>>>>>>> txq->stats
> >>>>>>>> values are from the master PMD. Those values are different and
> >>>>>>>> accounted separated from the values from the slave PMD.
> >>>>>>>>
> >>>>>>>> I see, since this is a little different than what most of the
> >>>>>>>> PMDs do, can you please put a little more info to the commit log?
> >>>>>>>> Or perhaps can add some comments to the code.
> >>>>>>>
> >>>>>>> Ok, will do.
> >>>>>>>
> >>>>>>>>
> >>>>>>>> And still 'stats->rx_nombuf' change is not required right? If
> >>>>>>>> so can you remove it in the next version?
> >>>>>>>
> >>>>>>> It is still needed. NETVSC unconditionally calls the slave PMD
> >>>>>>> to receive
> >>>>>> packets, even if it can't allocate a mbuf to receive a synthetic
> >>>>>> packet itself. The accounting of rx_nombuf is valid because the
> >>>>>> synthetic packets (to NETVSC) and VF packets (to slave PMD) are
> >>>>>> routed
> >> separately from Hyper-V.
> >>>>>>
> >>>>>> I am not referring to the "+=" update, my comment was because
> >>>>>> 'stats-
> >>>>>>> rx_nombuf' is overwritten in 'rte_eth_stats_get()' [1].
> >>>>>> Is it still required?
> >>>>>
> >>>>> Yes, it is still needed. NETVSC calls the rte_eth_stats_get() on
> >>>>> its slave PMD
> >> first, and stats->rx_nombuf is updated (overwritten) for its slave
> >> PMD. Afte that, it needs to add to its own
> >> dev->data->rx_mbuf_alloc_failed back to stats-
> >>> rx_nombuf.
> >>>>>
> >>>>
> >>>> But its own stat also will be overwritten (not in PMD function, but
> >>>> in ethdev layer).
> >>>> 'stats->rx_nombuf' assignment in the PMD seems has no effect and
> >>>> can be removed.
> >>>>
> >>>> I can't see how it is needed, can you please put a call stack to describe?
> >>>
> >>> This here:
> >>>
> >>>
> >>> int
> >>> rte_eth_stats_get(uint16_t port_id, struct rte_eth_stats *stats) {
> >>> 	struct rte_eth_dev *dev;
> >>>
> >>> 	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
> >>> 	dev = &rte_eth_devices[port_id];
> >>>
> >>> 	if (stats == NULL) {
> >>> 		RTE_ETHDEV_LOG(ERR, "Cannot get ethdev port %u stats to
> >> NULL\n",
> >>> 			port_id);
> >>> 		return -EINVAL;
> >>> 	}
> >>>
> >>> 	memset(stats, 0, sizeof(*stats));
> >>>
> >>> 	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->stats_get, -ENOTSUP);
> >>> 	stats->rx_nombuf = dev->data->rx_mbuf_alloc_failed;
> >>> 	return eth_err(port_id, (*dev->dev_ops->stats_get)(dev, stats)); }
> >>>
> >>> Will fill in rx_nombuf from the current rx_mbuf_alloc_failed.
> >>> But it happens before the PMD specific stats function.
> >>>
> >>
> >> I keep seeing the ethdev assignment as *after* the dev_ops, but it is
> >> not [1], so code is OK as it is.
> >
> > Hi Ferruh,
> >
> > Do you still want me to send a v3, or this patch is good as it is?
> >
> 
> Yes can you please send a v3 with some more description in the commit log on
> the special case for the PMD, and perhaps some comments in the code.
> 
> Thanks,
> Ferruh

Yes, will send out shortly.