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

[Alexander Lobakin]

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@xxxxxxxx>
> > > 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@xxxxxxxx>
> > > > Acked-by: Edward Cree <ecree@xxxxxxxxxxxxxx>
> > >
> > > Applied, thank you.
> >
> > David, Edward, Eric, Ilias,
> > thank you for your time.
> >
> > Regards,
> > á á á á á á
>
> 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,
á á á á á á