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

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

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"?

> on 48 bit limitation by enlarging the limitation.
> 
> Fixes: 4861cde46116 ("i40e: new poll mode driver")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Junyu Jiang <junyux.jiang@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.

Also can you please confirm the initial value of the 
"vsi->offset_loaded" is correct.

<....>

> @@ -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.


>   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)?