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

[Alexander Lobakin]

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@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. :)

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,
> á á á á á á

Regards,
á á á á á á