netdev - Re: [PATCH net-next] r8152: divide the tx and rx bottom functions

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Date:   Fri, 16 Aug 2019 11:27:11 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Hayes Wang <hayeswang@...ltek.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] r8152: divide the tx and rx bottom functions



On 8/16/19 11:08 AM, Hayes Wang wrote:
> Eric Dumazet [mailto:eric.dumazet@...il.com]
>> Sent: Friday, August 16, 2019 4:20 PM
> [...]
>> Which callback ?
> 
> The USB device has two endpoints for Tx and Rx.
> If I submit tx or rx URB to the USB host controller,
> the relative callback functions would be called, when
> they are finished. For rx, it is read_bulk_callback.
> For tx, it is write_bulk_callback.
> 
>> After an idle period (no activity, no prior packets being tx-completed ...),
>> a packet is sent by the upper stack, enters the ndo_start_xmit() of a network
>> driver.
>>
>> This driver ndo_start_xmit() simply adds an skb to a local list, and returns.
> 
> Base on the current method (without tasklet), when
> ndo_start_xmit() is called, napi_schedule is called only
> if there is at least one free buffer (!list_empty(&tp->tx_free))
> to transmit the packet. Then, the flow would be as following.

Very uncommon naming conventions really :/


Maybe you would avoid messing with a tasklet (we really try to get rid
of tasklets in general) using two NAPI, one for TX, one for RX.

Some drivers already use two NAPI, it is fine.

This might avoid the ugly dance in r8152_poll(),
calling napi_schedule(napi) after napi_complete_done() !