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

["Jiang, JunyuX" <junyux.jiang@intel.com>]

Hi Ferruh,

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Wednesday, September 16, 2020 8:31 PM
> To: Jiang, JunyuX <junyux.jiang@intel.com>; dev@dpdk.org
> Cc: Guo, Jia <jia.guo@intel.com>; Xing, Beilei <beilei.xing@intel.com>;
> stable@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@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.
> 
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 .

> 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.