netdev - Re: question about using UDP GSO in Linux kernel 4.19

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Message-ID: <CA+FuTSddWpsor8n8WaDkR-f=843SVs6SiLXU_E-yRCctDDkg3g@mail.gmail.com>
Date:   Sun, 26 Jul 2020 14:45:19 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Han <keepsimple@...il.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: question about using UDP GSO in Linux kernel 4.19

On Sun, Jul 26, 2020 at 2:18 PM Han <keepsimple@...il.com> wrote:
>
> On Sun, Jul 26, 2020 at 6:42 AM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > On Sat, Jul 25, 2020 at 7:08 PM Han <keepsimple@...il.com> wrote:
> > >
> > > My apologies if this is not the right place to ask this question.
> > >
> > > I'm trying to use UDP GSO to improve the throughput. My testing shows
> > > that UDP GSO works with the local server (i.e. loopback interface) but
> > > fails with a remote server (in WLAN, via wlan0 interface).
> > >
> > > My question is: do I need to explicitly enable UDP GSO for wlan0
> > > interface? If yes, how do I do it? I searched online but could not
> > > find a good answer.  I looked at "ethtool" but not clear which option
> > > to use:
> > >
> > > $ ethtool  --show-offload wlan0 | grep -i generic-segment
> > > generic-segmentation-offload: off [requested on]
> >
> > Which wireless driver does your device use. Does it have tx checksum offload?
>
> It seems to be "brcmfmac" :
>
> $ readlink /sys/class/net/wlan0/device/driver
> ../../../../../../../../bus/sdio/drivers/brcmfmac
>
> I think tx checksum offload is off, and I couldn't turn it on. Does
> "[fixed]" mean it cannot be changed?

Indeed. That explains it.