netdev - Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO

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Date:   Wed, 27 Nov 2019 22:28:57 +0300
From:   Alexander Lobakin <alobakin@...nk.ru>
To:     David Miller <davem@...emloft.net>
Cc:     ecree@...arflare.com, jiri@...lanox.com, edumazet@...gle.com,
        idosch@...lanox.com, pabeni@...hat.com, petrm@...lanox.com,
        sd@...asysnail.net, f.fainelli@...il.com,
        jaswinder.singh@...aro.org, manishc@...vell.com,
        GR-Linux-NIC-Dev@...vell.com, johannes.berg@...el.com,
        emmanuel.grumbach@...el.com, luciano.coelho@...el.com,
        linuxwifi@...el.com, kvalo@...eaurora.org,
        nicholas.johnson-opensource@...look.com.au, kenny@...ix.com,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet
 stalling

David Miller wrote 27.11.2019 22:23:
> From: Alexander Lobakin <alobakin@...nk.ru>
> Date: Wed, 27 Nov 2019 12:41:23 +0300
> 
>> Commit 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
>> napi_gro_receive()") has applied batched GRO_NORMAL packets processing
>> to all napi_gro_receive() users, including mac80211-based drivers.
>> 
>> However, this change has led to a regression in iwlwifi driver [1][2] 
>> as
>> it is required for NAPI users to call napi_complete_done() or
>> napi_complete() and the end of every polling iteration, whilst iwlwifi
>> doesn't use NAPI scheduling at all and just calls napi_gro_flush().
>> In that particular case, packets which have not been already flushed
>> from napi->rx_list stall in it until at least next Rx cycle.
>> 
>> Fix this by adding a manual flushing of the list to iwlwifi driver 
>> right
>> before napi_gro_flush() call to mimic napi_complete() logics.
>> 
>> I prefer to open-code gro_normal_list() rather than exporting it for 2
>> reasons:
>> * to prevent from using it and napi_gro_flush() in any new drivers,
>>   as it is the *really* bad way to use NAPI that should be avoided;
>> * to keep gro_normal_list() static and don't lose any CC 
>> optimizations.
>> 
>> I also don't add the "Fixes:" tag as the mentioned commit was only a
>> trigger that only exposed an improper usage of NAPI in this particular
>> driver.
>> 
>> [1] 
>> https://lore.kernel.org/netdev/PSXP216MB04388962C411CD0B17A86F47804A0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM
>> [2] https://bugzilla.kernel.org/show_bug.cgi?id=205647
>> 
>> Signed-off-by: Alexander Lobakin <alobakin@...nk.ru>
> 
> Applied, thanks for the quick turnaround.

Thank you all folks!

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ