netdev - RE: [PATCH net-next resend 1/2] r8152: remove queuing rx packets in driver

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Date: Mon, 18 Sep 2023 08:38:31 +0000
From: Hayes Wang <hayeswang@...ltek.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net"
	<davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org"
	<linux-usb@...r.kernel.org>,
        "bjorn@...k.no" <bjorn@...k.no>,
        "pabeni@...hat.com" <pabeni@...hat.com>
Subject: RE: [PATCH net-next resend 1/2] r8152: remove queuing rx packets in driver

Eric Dumazet <edumazet@...gle.com>
> Sent: Monday, September 18, 2023 3:55 PM
[...]
> >                         urb->actual_length = 0;
> >                         list_add_tail(&agg->list, next);
> >                 }
> > +
> > +               /* Break if budget is exhausted. */
> 
> [1] More conventional way to to put this condition at the beginning of
> the while () loop,
> because the budget could be zero.

If the budget is zero, the function wouldn't be called.
a7b8d60b3723 ("r8152: check budget for r8152_poll") avoids it.

> > +               if (work_done >= budget)
> > +                       break;
> >         }
> >
> > +       /* Splice the remained list back to rx_done */
> >         if (!list_empty(&rx_queue)) {
> >                 spin_lock_irqsave(&tp->rx_lock, flags);
> > -               list_splice_tail(&rx_queue, &tp->rx_done);
> > +               list_splice(&rx_queue, &tp->rx_done);
> >                 spin_unlock_irqrestore(&tp->rx_lock, flags);
> >         }
> >
> >  out1:
> > -       return work_done;
> > +       if (work_done > budget)
> 
> This (work_done >budget) condition would never be true if point [1] is
> addressed.

A bulk transfer may contain many packets, so the work_done may be more than budget.
That is why I queue the packets in the driver before this patch.
For example, if a bulk transfer contains 70 packet and budget is 64,
napi_gro_receive would be called for the first 64 packets and 6 packets would
be queued in driver for next schedule. After this patch, napi_gro_receive() would
be called for the 70 packets, even the budget is 64. And the remained bulk transfers
would be handled for next schedule.

> > +               return budget;
> > +       else
> > +               return work_done;
> >  }

Best Regards,
Hayes