netdev - Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in napi_gro

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Date:   Wed, 27 Nov 2019 10:47:26 +0300
From:   Alexander Lobakin <alobakin@...nk.ru>
To:     David Miller <davem@...emloft.net>
Cc:     pabeni@...hat.com, johannes@...solutions.net, ecree@...arflare.com,
        nicholas.johnson-opensource@...look.com.au, jiri@...lanox.com,
        edumazet@...gle.com, idosch@...lanox.com, petrm@...lanox.com,
        sd@...asysnail.net, f.fainelli@...il.com,
        jaswinder.singh@...aro.org, ilias.apalodimas@...aro.org,
        linux-kernel@...r.kernel.org, emmanuel.grumbach@...el.com,
        luciano.coelho@...el.com, linuxwifi@...el.com,
        kvalo@...eaurora.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in
 napi_gro_receive()

David Miller wrote 27.11.2019 02:57:
> From: Alexander Lobakin <alobakin@...nk.ru>
> Date: Mon, 25 Nov 2019 15:02:24 +0300
> 
>> Paolo Abeni wrote 25.11.2019 14:42:
>>> For -net, I *think* something as dumb and hacky as the following 
>>> could
>>> possibly work:
>>> ----
>>> diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>>> b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>>> index 4bba6b8a863c..df82fad96cbb 100644
>>> --- a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>>> +++ b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>>> @@ -1527,7 +1527,7 @@ static void iwl_pcie_rx_handle(struct iwl_trans
>>> *trans, int queue)
>>>                 iwl_pcie_rxq_alloc_rbs(trans, GFP_ATOMIC, rxq);
>>>         if (rxq->napi.poll)
>>> -               napi_gro_flush(&rxq->napi, false);
>>> +               napi_complete_done(&rxq->napi, 0);
>>>         iwl_pcie_rxq_restock(trans, rxq);
>>>  }
>>> ---
>> 
>> napi_complete_done(napi, 0) has an equivalent static inline
>> napi_complete(napi). I'm not sure it will work without any issues
>> as iwlwifi doesn't _really_ turn NAPI into scheduling state.
>> 
>> I'm not very familiar with iwlwifi, but as a work around manual
>> napi_gro_flush() you can also manually flush napi->rx_list to
>> prevent packets from stalling:
>> 
>> diff -Naur a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>> b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
>> --- a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c 2019-11-25
>> --- 14:55:03.610355230 +0300
>> +++ b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c 2019-11-25
>> 14:57:29.399556868 +0300
>  ...
> 
> Thanks to everyone for looking into this.
> 
> Can I get some kind of fix in the next 24 hours?  I want to send a 
> quick
> follow-on pull request to Linus to deal with all of the fallout, and in
> particular fix this regression.

If Intel guys and others will agree, I'll send a patch which will add
manual napi->rx_list flushing in iwlwifi driver in about ~2-3 hours.

Anyway, this driver should get a proper NAPI in future releases to
prevent problems like this one.

> Thanks!

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ