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

[Igor Ryzhov]

Hi,

Your code will work only if stats are updated at least once between two
overflows.
So it's still up to the application to handle this properly. I think it
should be mentioned in the docs.

Igor

On Fri, Sep 18, 2020 at 6:45 AM Jiang, JunyuX <junyux.jiang at intel.com>
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 .
>
> > 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.
>