netdev - Re: [PATCH net-next 3/3] eth: bnxt: handle invalid Tx completions more gracefully

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Date: Tue, 11 Jul 2023 21:11:02 -0700
From: Michael Chan <michael.chan@...adcom.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com, 
	pabeni@...hat.com
Subject: Re: [PATCH net-next 3/3] eth: bnxt: handle invalid Tx completions
 more gracefully

On Tue, Jul 11, 2023 at 6:09 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 11 Jul 2023 17:01:08 -0700 Michael Chan wrote:
> > > It generally looks good to me.  I have a few comments below.
> > >
> > > The logic is very similar to the bnapi->in_reset logic to reset due to
> > > RX errors.  We have a counter for the number of times we do the RX
> > > reset so I think it might be good to add a similar TX reset counter.
> >
> > Never mind about the counter.  Since we are doing a complete reset,
> > the cpr structure will be freed anyway and the counter won't persist.
> >
> > Later when we add support for per TX ring reset, we can add the
> > counter at that time.
>
> Oh, if all the cpr stats get lost during reset or re-config, that's
> quite unfortunate. We should get that fixed without waiting for per
> ring resets of any sort, just in case that takes long.
>
> Can we stash the old sum somewhere and report in ethtool as "non-ring"
> or "old" or ..?
>

These are all the software stats that will be reset during a complete reset:

struct bnxt_rx_sw_stats {
        u64                     rx_l4_csum_errors;
        u64                     rx_resets;
        u64                     rx_buf_errors;
        u64                     rx_oom_discards;
        u64                     rx_netpoll_discards;
};

struct bnxt_cmn_sw_stats {
        u64                     missed_irqs;
};

These are per ring counters.  During complete reset, we free the ring
and allocate a new ring.  So re-applying these counters to the new
ring doesn't make sense because the new ring is not necessarily the
same as the old one.  So I think we'll need to have a total for each
of these and we'll save the snapshot of the total before reset and
restore the snapshot after reset.  Does that make sense?

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