[dpdk-stable] [PATCH v2] net/i40e: fix incorrect byte counters

[Ferruh Yigit]

On 9/18/2020 4:44 AM, Jiang, JunyuX wrote:
> Hi Ferruh,
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit at intel.com>
>> Sent: Wednesday, September 16, 2020 8:31 PM
>> To: Jiang, JunyuX <junyux.jiang at intel.com>; dev at dpdk.org
>> Cc: Guo, Jia <jia.guo at intel.com>; Xing, Beilei <beilei.xing at intel.com>;
>> stable at dpdk.org
>> Subject: Re: [dpdk-stable] [PATCH v2] net/i40e: fix incorrect byte counters
>>
>> On 9/16/2020 2:51 AM, Junyu Jiang wrote:
>>> This patch fixed the issue that rx/tx bytes overflowed
>>
>> "Rx/Tx statistics counters overflowed"?
>>
> Yes, the rx_bytes and tx_bytes counter in X710 cards is 48-bit long, if keep sending packets for a log time, the register will overflow.
> 
>>> on 48 bit limitation by enlarging the limitation.
>>>
>>> Fixes: 4861cde46116 ("i40e: new poll mode driver")
>>> Cc: stable at dpdk.org
>>>
>>> Signed-off-by: Junyu Jiang <junyux.jiang at intel.com>
>>> ---
>>>    drivers/net/i40e/i40e_ethdev.c | 47
>> ++++++++++++++++++++++++++++++++++
>>>    drivers/net/i40e/i40e_ethdev.h |  9 +++++++
>>>    2 files changed, 56 insertions(+)
>>>
>>> diff --git a/drivers/net/i40e/i40e_ethdev.c
>>> b/drivers/net/i40e/i40e_ethdev.c index 563f21d9d..4d4ea9861 100644
>>> --- a/drivers/net/i40e/i40e_ethdev.c
>>> +++ b/drivers/net/i40e/i40e_ethdev.c
>>> @@ -3073,6 +3073,13 @@ i40e_update_vsi_stats(struct i40e_vsi *vsi)
>>>    	i40e_stat_update_48(hw, I40E_GLV_BPRCH(idx),
>> I40E_GLV_BPRCL(idx),
>>>    			    vsi->offset_loaded, &oes->rx_broadcast,
>>>    			    &nes->rx_broadcast);
>>> +	/* enlarge the limitation when rx_bytes overflowed */
>>> +	if (vsi->offset_loaded) {
>>> +		if (I40E_RXTX_BYTES_LOW(vsi->old_rx_bytes) > nes-
>>> rx_bytes)
>>> +			nes->rx_bytes += (uint64_t)1 << I40E_48_BIT_WIDTH;
>>> +		nes->rx_bytes += I40E_RXTX_BYTES_HIGH(vsi-
>>> old_rx_bytes);
>>> +	}
>>> +	vsi->old_rx_bytes = nes->rx_bytes;
>>
>>
>> Can you please describe this logic? (indeed better to describe it in the
>> commit log)
>>
>> 'nes->rx_bytes' is diff in the stats register since last read.
>> 'old_rx_bytes' is the previous stats diff.
>>
>> Why/how "I40E_RXTX_BYTES_LOW(vsi->old_rx_bytes) > nes->rx_bytes" has
>> a meaning? Isn't this very depends on the read frequency?
>>
>> I guess I am missing something but please help me understand.
>>
> This patch fixes the issue of rx/tx bytes counter register overflow:
> The counter register in i40e is 48-bit long, when overflow, nes->rx_bytes becomes less than old_rx_bytes, the correct value of nes->rx_bytes should be plused 1 << 48.
> Use I40E_RXTX_BYTES_HIGH() to remember the MSB, nes->rx_bytes plus the MSB is the correct value, So that using uint64_t to enlarge the 48 bit  limitation of register .
 >

My bad, 'nes->rx_bytes' is NOT diff in the stats register since last 
read, it is accumulated stats value since last reset. Above logic make 
sense now.

What do you think creating a function something like 
'i40e_stat_update_48_in_64()' and hide all the extension inside it?
I think it reduces the clutter.

> 
>> Also can you please confirm the initial value of the "vsi->offset_loaded" is
>> correct.
>>
> offset_loaded will be true when get statistics of  port and offset_loaded will be false when reset or clear the statistics,
> so if  offset_loaded is false, shouldn't to calculate the value of nes->rx_bytes, it will be 0.
> 
>> <....>
>>
>>> @@ -282,6 +282,9 @@ struct rte_flow {
>>>    #define I40E_ETH_OVERHEAD \
>>>    	(RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN +
>> I40E_VLAN_TAG_SIZE * 2)
>>>
>>> +#define I40E_RXTX_BYTES_HIGH(bytes) ((bytes) & ~I40E_48_BIT_MASK)
>>> +#define I40E_RXTX_BYTES_LOW(bytes) ((bytes) & I40E_48_BIT_MASK)
>>> +
>>
>> HIGH/LOW is a little misleading, for 64Bits it sounds like it is getting low 32 bits
>> and high 32 bits, can you please clarify macro masks out
>> 48/16 bits.
>>
> Yes, I will change the macro name in V3.
>>
>>>    struct i40e_adapter;
>>>    struct rte_pci_driver;
>>>
>>> @@ -399,6 +402,8 @@ struct i40e_vsi {
>>>    	uint8_t vlan_anti_spoof_on; /* The VLAN anti-spoofing enabled */
>>>    	uint8_t vlan_filter_on; /* The VLAN filter enabled */
>>>    	struct i40e_bw_info bw_info; /* VSI bandwidth information */
>>> +	uint64_t old_rx_bytes;
>>> +	uint64_t old_tx_bytes;
>>
>> 'prev' seems better naming than 'old', what do you think renaming
>> 'old_rx_bytes' -> 'prev_rx_bytes' (for all variables)?
> Yes, it's better, I will fix it in V3.
>