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Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped

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On Mon, 2016-04-11 at 09:55 +0200, Bjørn Mork wrote:
> Ben Hutchings <ben@decadent.org.uk> writes:
> > 
> > On Sun, 2016-04-10 at 11:15 -0700, Vagrant Cascadian wrote:
> > > 
> > > It works for the most part, but floods syslog with messages:
> > > 
> > > [501966.870273] net_ratelimit: 35702 callbacks suppressed
> > > [501966.875438] smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped
> > > 
> > > It seems to function ok, though I'm not sure if there's degraded
> > > network performance...
> > [...]
> > 
> > I understand network performance on all RPi models is poor due to lack
> > of a built-in Ethernet MAC and the poor design of the USB interface.
> > Also that message is a generic error message from the usbnet core and
> > is not specific to the smsc95xx driver.
> Yes, kevent 2 is "EVENT_RX_MEMORY", and this error affects any usbnet
> based device under memory pressure.  The usbnet framework just doesn't
> handle the case where GFP_KERNEL allocations fail. How could it? 

What I don't understand, given this, is why Vagrant didn't report any
OOM warnings.  (I wondered whether the __GFP_NOWARN flag was wrongly
being added somewhere, but I don't see that.)

> The only viable "fix" I can see is by preallocating and recycling all
> buffers instead of the repeated allocations done by usbnet now.  But
> that's a major refactoring of usbnet.
> 
> The log message spam could of course be fixed, but the rate-limiting is
> "good enough".

How is anyone supposed to know what "kevent 2" is though?

The drivers that support batching into large RX buffers should
automatically fall back to smaller buffers if this happens, or whenever
they're running on a small (for some definition of small) machine.  I
understand that the dynamic fallback may be tricky though.

Ben.

-- 
Ben Hutchings
Humans are not rational beings; they are rationalising beings.

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Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-04-10 20:20 +0200
  Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-04-10 21:20 +0200
    Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-04-10 22:30 +0200
    Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Diederik de Haas <didi.debian@cknow.org> - 2016-04-10 23:00 +0200
      Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-04-11 02:20 +0200
        Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-04-11 03:10 +0200
          Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-04-11 17:20 +0200
          Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-04-13 20:50 +0200
            Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-04-28 17:20 +0200
              Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Diederik de Haas <didi.debian@cknow.org> - 2016-04-28 17:40 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-04-28 18:20 +0200
              Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-05-02 03:30 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-05-02 21:00 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-05-03 06:10 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Vagrant Cascadian <vagrant@debian.org> - 2016-05-03 18:20 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-05-07 13:50 +0200
                Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Diederik de Haas <didi.debian@cknow.org> - 2016-05-07 14:10 +0200
  Processed: Re: Bug#820622: linux-image-4.5.0-trunk-armmp-lpae:  raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped owner@bugs.debian.org (Debian Bug Tracking System) - 2016-04-10 21:20 +0200
  Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Bjørn Mork <bjorn@mork.no> - 2016-04-11 10:20 +0200
    Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Ben Hutchings <ben@decadent.org.uk> - 2016-04-11 13:30 +0200
      Bug#820622: linux-image-4.5.0-trunk-armmp-lpae: raspberry pi 2: smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped Bjørn Mork <bjorn@mork.no> - 2016-04-11 15:10 +0200
  Processed: Re: Bug#820622: linux-image-4.5.0-trunk-armmp-lpae:  raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped owner@bugs.debian.org (Debian Bug Tracking System) - 2016-04-28 17:20 +0200
  Processed: Re: Bug#820622: linux-image-4.5.0-trunk-armmp-lpae:  raspberry pi 2:  smsc95xx 1-1.1:1.0 eth0: kevent 2 may have been dropped owner@bugs.debian.org (Debian Bug Tracking System) - 2016-05-02 03:30 +0200

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