Re: [Bloat] Kirkwood BQL?

[Rosen Penev <rosenp@gmail.com>]

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My main question was why BQL support is not in the driver. I've seen it
listed on the bloated drivers page for a long time but no real explanation
why it remains so. I guess no interested party has the equipment to test
and verify if it works correctly. I will try to compile my own kernel with
the patch applied( current one has no codel compiled in) and see if any
issues occur. I know that TSO support is totally broken with this driver
(see: http://archlinuxarm.org/forum/viewtopic.php?f=9&t=7692&start=20 ). If
only it didn't take a day to compile :\.

On Wed, Jul 29, 2015, 10:42 Dave Taht <dave.taht@gmail.com> wrote:

> On Wed, Jul 29, 2015 at 7:07 PM, David Lang <david@lang.hm> wrote:
> > On Wed, 29 Jul 2015, Alan Jenkins wrote:
> >
> >> On 29/07/15 12:24, Alan Jenkins wrote:
> >>>
> >>> On 29/07/15 05:32, Rosen Penev wrote:
> >>>>
> >>>> Anyone know what the situation is with kirkwood and BQL? I found a
> >>>> patch for it but have no idea if there are any issues.
> >>>>
> >>>> I have such a system but have no idea how to ascertain the efficacy of
> >>>> BQL.
> >>>
> >>>
> >>> To the latter:
> >>>
> >>> BQL works for transmissions that reach the full line rate (e.g. for
> >>> 1000MB ethernet).  It limits the queue that builds in the
> driver/device to
> >>> the minimum they need.  Then queue mostly builds in the generic
> networking
> >>> stack, where it can be managed effectively e.g. by fq_codel.
> >>>
> >>> So a simple efficacy test is to run a transmission at full speed, and
> >>> monitor latency (ping) at the same time.  Just make sure the device
> qdisc is
> >>> set to fq_codel.  fq_codel effectively prioritizes ping, so the
> difference
> >>> will be very easy to see.
> >>>
> >>> I don't know if there's any corner cases that want testing as well.
> >
> >
> > BQL adjusts the number of packets that can be queued based on their
> size, so
> > you can have far more 64 byte packets queued than you can have 1500 byte
> > packets.
> >
> > do a ping flood of your network with different packet sizes and look at
> the
> > queue lengths that are allowed, the queue length should be much higher
> with
> > small packets.
> >
> >>> BQL can be disabled at runtime for comparison testing:
> >>> http://lists.openwall.net/netdev/2011/12/01/112
> >>>
> >>> There's a BQL tool to see it working graphically (using readouts from
> the
> >>> same sysfs directory):
> >>> https://github.com/ffainelli/bqlmon
> >>>
> >>> My Kirkwood setup at home is weak, I basically never reach full link
> >>> speed. So this might be somewhat academic unless you set the link
> speed to
> >>> 100 or 10 using the ethtool command.  (It seems like a good idea to
> test
> >>> those speeds even if you can do better though).  You probably also
> want to
> >>> start with offloads (tso, gso, gro) disabled using ethtool, because
> they
> >>> aggregate packets.
> >>>
> >>
> >> a quick test with a 100M setting, connected to gigabit switch, and flent
> >> tcp_download, shows ping under load increases to about 8ms. Conclusion:
> the
> >> Debian kirkwood kernel probably isn't doing BQL for me :).
>
> Wrong way I think. Try tcp_upload.
>
> >
> > 8ms of latency under load is doing very well. what are you expecting?
> >
> > David Lang
> >
> >
> >>> Flent can do this test and generate pretty graphs, including a time
> >>> series (plot type "all_scaled") and frequency distribution for the ping
> >>> ("ping_cdf").  Flent is a frontend to the netperf network performance
> >>> tester.  You could use a directly connected laptop and run your own
> netperf
> >>> server (netserver command).  You'll need to set up static IPs on both
> ends
> >>> for the duration... if headless then make sure you have an alternative
> >>> console access :).
> >>>
> >>> The normal Flent test is RRUL, which is two-way.  tcp_2up would be
> >>> better, to avoid testing both end's BQL at the same time.  If you want
> to
> >>> run tcp_2up the other way round, so you only need netserver on the
> ARM, try
> >>> using '--swap-up-down'.
> >>>
> >>> Alan
> >>
> >>
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>
>
> --
> Dave Täht
> worldwide bufferbloat report:
> http://www.dslreports.com/speedtest/results/bufferbloat
> And:
> What will it take to vastly improve wifi for everyone?
> https://plus.google.com/u/0/explore/makewififast
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