Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling

From: Alexander Lobakin <alobakin@dlink.ru>
To: Luciano Coelho <luciano.coelho@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Edward Cree <ecree@solarflare.com>,
	Jiri Pirko <jiri@mellanox.com>,
	Eric Dumazet <edumazet@google.com>,
	Ido Schimmel <idosch@mellanox.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Petr Machata <petrm@mellanox.com>,
	Sabrina Dubroca <sd@queasysnail.net>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Manish Chopra <manishc@marvell.com>,
	GR-Linux-NIC-Dev@marvell.com,
	Johannes Berg <johannes.berg@intel.com>,
	Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
	Intel Linux Wireless <linuxwifi@intel.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>,
	"Kenneth R. Crudup" <kenny@panix.com>,
	netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling
Date: Wed, 27 Nov 2019 13:12:34 +0300	[thread overview]
Message-ID: <c571a88c15c4a70a61cde6ca270af033@dlink.ru> (raw)
In-Reply-To: <7a9332bf645fbb8c9fff634a3640c092fb9b4b79.camel@intel.com>

Luciano Coelho wrote 27.11.2019 12:58:
> On Wed, 2019-11-27 at 12:41 +0300, Alexander Lobakin wrote:
>> 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@dlink.ru>
>> ---
> 
> We don't usually use "net: wireless: intel:" in the commit message, we
> would use "iwlwifi: pcie:", but I don't care much.
> 
> Otherwise:
> 
> Acked-by: Luca Coelho <luciano.coelho@intel.com>

Thank you!

> Thanks a lot for the fix!
> 
> Dave, I'm assuming you'll take this directly into your tree, right?

Also please let me know if I should send v2 with Ack and fixed commit
subject!

> --
> Cheers,
> Luca.

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ