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Date:   Mon, 25 Nov 2019 11:25:50 +0300
From:   Alexander Lobakin <alobakin@dlink.ru>
To:     Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Cc:     David Miller <davem@davemloft.net>, ecree@solarflare.com,
        jiri@mellanox.com, edumazet@google.com, idosch@mellanox.com,
        pabeni@redhat.com, petrm@mellanox.com, sd@queasysnail.net,
        f.fainelli@gmail.com, jaswinder.singh@linaro.org,
        ilias.apalodimas@linaro.org, linux-kernel@vger.kernel.org,
        johannes.berg@intel.com, emmanuel.grumbach@intel.com,
        luciano.coelho@intel.com, linuxwifi@intel.com,
        kvalo@codeaurora.org, netdev@vger.kernel.org,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2 net-next] net: core: use listified Rx for GRO_NORMAL in
 napi_gro_receive()
In-Reply-To: <c762f5eee08a8f2d0d6cb927d7fa3848@dlink.ru>
References: <20191014080033.12407-1-alobakin@dlink.ru>
 <20191015.181649.949805234862708186.davem@davemloft.net>
 <7e68da00d7c129a8ce290229743beb3d@dlink.ru>
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 <c762f5eee08a8f2d0d6cb927d7fa3848@dlink.ru>
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Alexander Lobakin wrote 25.11.2019 10:54:
> 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@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].
> 
> 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. :)

And you can also set /proc/sys/net/core/gro_normal_batch to the value
of 1 and see if there are any changes. This value makes GRO stack to
behave just like without the patch.

>> Kind regards,
>> Nicholas Johnson
> 
> Regards,
> ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ

Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ