netdev - Re: tg3 dropping packets at high packet rates

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Date:   Sun, 22 May 2022 16:22:10 -0700
From:   Michael Chan <michael.chan@...adcom.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mchan@...adcom.com" <mchan@...adcom.com>,
        David Miller <davem@...emloft.net>,
        Pavan Chebbi <pavan.chebbi@...adcom.com>
Subject: Re: tg3 dropping packets at high packet rates

On Thu, May 19, 2022 at 1:44 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Michael Chan
> > Sent: 19 May 2022 01:52
> > Please show a snapshot of all the counters.  In particular,
> > rxbds_empty, rx_discards, etc will show whether the driver is keeping
> > up with incoming RX packets or not.
>
> After running the test for a short time.
> The application stats indicate that around 40000 packets are missing.
>
> # ethtool -S em2 | grep -v ' 0$'; for f in /sys/class/net/em2/statistics/*; do echo $f $(cat $f); done|grep -v ' 0$'
> NIC statistics:
>      rx_octets: 4589028558
>      rx_ucast_packets: 21049866
>      rx_mcast_packets: 763
>      rx_bcast_packets: 746
>      tx_octets: 4344
>      tx_ucast_packets: 6
>      tx_mcast_packets: 40
>      tx_bcast_packets: 3
>      rxbds_empty: 76

This means that the RX ring became empty (with no RX BDs) 76 times.
It doesn't necessarily mean packets were dropped yet because the chip
will continue to buffer using on-chip buffers.

>      rx_discards: 14

But this means that 14 packets were dropped because on-chip buffers
were full.  I don't know why it is not matching the 40000 missing
packets reported by the application.

>      mbuf_lwm_thresh_hit: 14

This means that the low on-chip buffer threshold was crossed 14 times.
This should trigger pause frames to be sent if flow control is
enabled.

> /sys/class/net/em2/statistics/multicast 763
> /sys/class/net/em2/statistics/rx_bytes 4589028558
> /sys/class/net/em2/statistics/rx_missed_errors 14
> /sys/class/net/em2/statistics/rx_packets 21433169
> /sys/class/net/em2/statistics/tx_bytes 4344
> /sys/class/net/em2/statistics/tx_packets 49
>

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