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

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

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.


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