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

[Ferruh Yigit <ferruh.yigit@xilinx.com>]

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

> Long
> 
>>
>>
>> [1]
>> It seems assignment was after but it is fixed on the way:
>> Commit 53ecfa24fbcd ("ethdev: fix overwriting driver-specific stats")