netdev - 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 10:54:44 +0300
From:   Alexander Lobakin <alobakin@...nk.ru>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
Cc:     David Miller <davem@...emloft.net>, 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,
        ilias.apalodimas@...aro.org, netdev@...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()

Nicholas Johnson wrote 25.11.2019 10:29:
> 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].

Hi!

It's a bit strange as this commit doesn't directly affect the packet
flow. I don't have any iwlwifi hardware at the moment, so let's see if
anyone else will be able to reproduce this (for now, it is the first
report in a ~6 weeks after applying to net-next).
Anyway, I'll investigate iwlwifi's Rx processing -- maybe I could find
something driver-specific that might produce this.

Thank you for the report.

> 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

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ