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

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Date:   Mon, 25 Nov 2019 07:29:22 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     Alexander Lobakin <alobakin@...nk.ru>
CC:     David Miller <davem@...emloft.net>,
        "ecree@...arflare.com" <ecree@...arflare.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "idosch@...lanox.com" <idosch@...lanox.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "petrm@...lanox.com" <petrm@...lanox.com>,
        "sd@...asysnail.net" <sd@...asysnail.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "jaswinder.singh@...aro.org" <jaswinder.singh@...aro.org>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in
 napi_gro_receive()

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@...nk.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@...nk.ru>
> > > Acked-by: Edward Cree <ecree@...arflare.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