[dpdk-dev] [PATCH v2 1/2] net/i40e: fix clear xstats bug in vf port

[Ferruh Yigit]

On 9/1/2017 3:30 AM, Zhao1, Wei wrote:
> Hi,  Ferruh
> 
>> -----Original Message-----
>> From: Yigit, Ferruh
>> Sent: Friday, September 1, 2017 12:54 AM
>> To: Zhao1, Wei <wei.zhao1 at intel.com>; dev at dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v2 1/2] net/i40e: fix clear xstats bug in vf
>> port
>>
>> On 8/29/2017 3:28 AM, Wei Zhao wrote:
>>> There is a bug in vf clear xstats command, it do not record the
>>> statics data in offset struct member.So, vf need to keep record of
>>> xstats data from pf and update the statics according to offset.
>>>
>>> Fixes: da61cd0849766 ("i40evf: add extended stats")
>>>
>>> Signed-off-by: Wei Zhao <wei.zhao1 at intel.com>
>>>
>>> ---
>>>
>>> Changes in v2:
>>>
>>>  fix patch log check warning.
>>> ---
>>>  app/test-pmd/config.c             |  6 ++--
>>>  drivers/net/i40e/i40e_ethdev_vf.c | 64
>>> ++++++++++++++++++++++++++++++++++++++-
>>>  2 files changed, 67 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/app/test-pmd/config.c b/app/test-pmd/config.c index
>>> 3ae3e1c..14131d6 100644
>>> --- a/app/test-pmd/config.c
>>> +++ b/app/test-pmd/config.c
>>> @@ -203,8 +203,10 @@ nic_stats_display(portid_t port_id)
>>>  	if (diff_cycles > 0)
>>>  		diff_cycles = prev_cycles[port_id] - diff_cycles;
>>>
>>> -	diff_pkts_rx = stats.ipackets - prev_pkts_rx[port_id];
>>> -	diff_pkts_tx = stats.opackets - prev_pkts_tx[port_id];
>>> +	diff_pkts_rx = (stats.ipackets > prev_pkts_rx[port_id]) ?
>>> +		(stats.ipackets - prev_pkts_rx[port_id]) : 0;
>>> +	diff_pkts_tx = (stats.opackets > prev_pkts_tx[port_id]) ?
>>> +		(stats.opackets - prev_pkts_tx[port_id]) : 0;
>>
>> I guess this testpmd update is not directly related to this patch, but to protect
>> testpmd against value overflow? Can this be another patch?
> 
> Nonono, this code change is directly related to this patch, if we do not do this code change, the  
> diff_pkts_rx and diff_pkts_tx statistic data will be wrong  when the first time after clear xstats command.

If this testpmd code is only wrong for i40e vf after this patch, perhaps
something else is wrong? Perhaps we should update i40e vf stats.

OR, if this code is already wrong, lets move it to its own patch.

> 
>>
>> <...>
>>
>>>  static int
>>>  i40evf_get_statistics(struct rte_eth_dev *dev, struct rte_eth_stats
>>> *stats)  {
>>>  	int ret;
>>>  	struct i40e_eth_stats *pstats = NULL;
>>> +	struct i40e_vf *vf = I40EVF_DEV_PRIVATE_TO_VF(dev->data-
>>> dev_private);
>>> +	struct i40e_vsi *vsi = &vf->vsi;
>>>
>>>  	ret = i40evf_update_stats(dev, &pstats);
>>>  	if (ret != 0)
>>>  		return 0;
>>>
>>> +	i40evf_update_vsi_stats(vsi, pstats);
>>
>> But not having this previously means all VF stats were wrong previously, not
>> only extended ones, also basic ones. And not not wrong with small
>> difference, this should give a big difference in the stats.
>>
>> I am suspicious about this part, because if this is the case, I would expect this
>> should be detected earlier.
>>
>> I have not traced the code, but is there any chance that "eth_stats_offset"
>> has been used by other end of the admin command?
> 
> To be frankly speaking, this bug is firstly discovered by a big user.
> This bug only appear after use CLI "clear port xstats 0". So it is not easy to detect this bug.
> After using this fix patch ,the big user who report this issue has feed back it work well now.
> The root cause is not so complicated, when the pf which admin this vf is in kernel state, DPDK can not 
> Give pf the info to clear and update offset command, so vf can only keep record the offset data in DPDK
> VF port locally.

Please help me understand this.

1- The problem you are fixing only seen with Linux PF, with DPDK PF you
don't see the problem, correct? If so this should be part of commit log.

2- As I checked the Linux driver code, it does same thing with DPDK:
a) in PF side, read from registers
b) removed vsi->eth_stats_offsets from read values
c) set vsi->eth_stats
So vsi->eth_stats should be valid, can you please elaborate the issue
with Linux PF.

3- This patch introduces i40evf_update_vsi_stats(), which removes
vsi->eth_stats_offset from stats received from PF.
But for DPDK PF case, the stats received from PF are already removes
vsi->eth_stats_offset, won't this will be a duplicate, and give wrong
values for the DPDK PF case ?

4- Is VF stats registers, reset on read? I mean the received stats
values via i40evf_update_stats() are values from previous read, or
cumulative values?

> 
> 
>>
>>> +
>>>  	stats->ipackets = pstats->rx_unicast + pstats->rx_multicast +
>>>  						pstats->rx_broadcast;
>>>  	stats->opackets = pstats->tx_broadcast + pstats->tx_multicast + @@
>>> -1025,7 +1083,7 @@ i40evf_dev_xstats_reset(struct rte_eth_dev *dev)
>>>  	i40evf_update_stats(dev, &pstats);
>>>
>>>  	/* set stats offset base on current values */
>>> -	vf->vsi.eth_stats_offset = vf->vsi.eth_stats;
>>> +	vf->vsi.eth_stats_offset = *pstats;
>>
>> I can see this is the reason of the defect mentioned in the commit log.
>> Instead of using newly acquired stats as offset, using old values...

After some more digging, "vf->vsi.eth_stats" and "*pstats" should be
same, i40evf_update_stats() both updates the "vf->vsi.eth_stats" and
returns its pointer [1], so why this update needed.

[1]
i40e_pf_host_process_cmd_get_stats() {
...
	i40e_pf_host_send_msg_to_vf(vf, VIRTCHNL_OP_GET_STATS,
		I40E_SUCCESS,
		(uint8_t *)&vf->vsi->eth_stats,
		sizeof(vf->vsi->eth_stats));
...


>>
>> <...>