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

[Ferruh Yigit]

On 9/18/2020 10:23 AM, Igor Ryzhov wrote:
> Hi,
> 
> Your code will work only if stats are updated at least once between two 
> overflows.
 >

In this case it will have problems in 'i40e_stat_update_48()' too.
It seems there is no way to detect if the increase in stats is N or 
MAX_48+N by the software.
And obviously there is no way to detect if the overflow occurred more 
than once.

> So it's still up to the application to handle this properly. I think it 
> should be mentioned in the docs.
> 

+1 to document.

> Igor
> 
> On Fri, Sep 18, 2020 at 6:45 AM Jiang, JunyuX <junyux.jiang at intel.com 
> <mailto:junyux.jiang at intel.com>> wrote:
> 
>     Hi Ferruh,
> 
>      > -----Original Message-----
>      > From: Ferruh Yigit <ferruh.yigit at intel.com
>     <mailto:ferruh.yigit at intel.com>>
>      > Sent: Wednesday, September 16, 2020 8:31 PM
>      > To: Jiang, JunyuX <junyux.jiang at intel.com
>     <mailto:junyux.jiang at intel.com>>; dev at dpdk.org <mailto:dev at dpdk.org>
>      > Cc: Guo, Jia <jia.guo at intel.com <mailto:jia.guo at intel.com>>;
>     Xing, Beilei <beilei.xing at intel.com <mailto:beilei.xing at intel.com>>;
>      > stable at dpdk.org <mailto: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 <mailto:stable at dpdk.org>
>      > >
>      > > Signed-off-by: Junyu Jiang <junyux.jiang at intel.com
>     <mailto: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.
>