Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in napi_gro_receive()

From: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
To: Alexander Lobakin <alobakin@dlink.ru>
Cc: David Miller <davem@davemloft.net>,
	"ecree@solarflare.com" <ecree@solarflare.com>,
	"jiri@mellanox.com" <jiri@mellanox.com>,
	"edumazet@google.com" <edumazet@google.com>,
	"idosch@mellanox.com" <idosch@mellanox.com>,
	"pabeni@redhat.com" <pabeni@redhat.com>,
	"petrm@mellanox.com" <petrm@mellanox.com>,
	"sd@queasysnail.net" <sd@queasysnail.net>,
	"f.fainelli@gmail.com" <f.fainelli@gmail.com>,
	"jaswinder.singh@linaro.org" <jaswinder.singh@linaro.org>,
	"ilias.apalodimas@linaro.org" <ilias.apalodimas@linaro.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in napi_gro_receive()
Date: Mon, 25 Nov 2019 07:29:22 +0000	[thread overview]
Message-ID: <PSXP216MB04388962C411CD0B17A86F47804A0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <7e68da00d7c129a8ce290229743beb3d@dlink.ru>

Hi,

On Wed, Oct 16, 2019 at 10:31:31AM +0300, Alexander Lobakin wrote:
> David Miller wrote 16.10.2019 04:16:
> > From: Alexander Lobakin <alobakin@dlink.ru>
> > Date: Mon, 14 Oct 2019 11:00:33 +0300
> > 
> > > Commit 323ebb61e32b4 ("net: use listified RX for handling GRO_NORMAL
> > > skbs") made use of listified skb processing for the users of
> > > napi_gro_frags().
> > > The same technique can be used in a way more common napi_gro_receive()
> > > to speed up non-merged (GRO_NORMAL) skbs for a wide range of drivers
> > > including gro_cells and mac80211 users.
> > > This slightly changes the return value in cases where skb is being
> > > dropped by the core stack, but it seems to have no impact on related
> > > drivers' functionality.
> > > gro_normal_batch is left untouched as it's very individual for every
> > > single system configuration and might be tuned in manual order to
> > > achieve an optimal performance.
> > > 
> > > Signed-off-by: Alexander Lobakin <alobakin@dlink.ru>
> > > Acked-by: Edward Cree <ecree@solarflare.com>
> > 
> > Applied, thank you.
> 
> David, Edward, Eric, Ilias,
> thank you for your time.
> 
> Regards,
> ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ

I am very sorry to be the bearer of bad news. It appears that this
commit is causing a regression in Linux 5.4.0-rc8-next-20191122,
preventing me from connecting to Wi-Fi networks. I have a Dell XPS 9370
(Intel Core i7-8650U) with Intel Wireless 8265 [8086:24fd].

I did a bisect, and this commit was named the culprit. I then applied
the reverse patch on another clone of Linux next-20191122, and it
started working.

6570bc79c0dfff0f228b7afd2de720fb4e84d61d
net: core: use listified Rx for GRO_NORMAL in napi_gro_receive()

You can see more at the bug report I filed at [0].

[0]
https://bugzilla.kernel.org/show_bug.cgi?id=205647

I called on others at [0] to try to reproduce this - you should not pull 
a patch because of a single reporter - as I could be wrong.

Please let me know if you want me to give more debugging information or 
test any potential fixes. I am happy to help to fix this. :)

Kind regards,
Nicholas Johnson