[Cerowrt-devel] BQL, txqueue lengths and the internet of things

[David P. Reed]

Maybe you can do a quick blog howto?  I'd bet the same could be done for raspberry pi and perhaps my other toy the wandboard which has a gigE adapter and Scsi making it a nice iscsi target or nfs server. 

De bloating the world... One step at a time.

On Jun 11, 2014, Dave Taht <dave.taht at gmail.com> wrote:
>The bloat problem and solutions are not just limited to fixing
>routers, but hosts.
>
>Nearly every low end board I've seen out there forgos a gigE ethernet
>interface in favor of a lower power and cost 100mbit interface.
>
>No distro I've seen modifies the default pfifo txqueuelen from the
>current 1000 packet default down to a more reasonable 100 packet
>default in that case. And, while many ethernet devices in this
>category are hooked up via usb (and currently hard to add BQL support
>to), some are not, and byte queue limit support can be easily added to
>those.
>
>Sadly byte queue limits (BQL) is only implemented on a bunch of top
>end ethernet drivers. (about 10, last I looked)
>
>I needed a break from big problems, so a couple late nights later, I
>have a very small patch adding support for BQL to the beaglebone
>black:
>
>http://snapon.lab.bufferbloat.net/~d/0001-Add-BQL-support-to-cpsw-beaglebone-driver.patch
>
>And the results were quite pleasing at 100mbit. BQL holds things down
>to two full size packets in the tx ring and we see an enormous
>improvement in bidirectional throughput, jitter, and latency.
>
>http://snapon.lab.bufferbloat.net/~d/beagle_bql/bql_makes_a_difference.png
>http://snapon.lab.bufferbloat.net/~d/beagle_bql/beaglebonewins.png
>
>The default linux behavior ( pfifo fast, txqueue 1000 ) prior to this
>patch looked pretty awful:
>
>http://snapon.lab.bufferbloat.net/~d/beagle_nobql/pfifo_nobql_tsq3028txqueue1000.svg
>
>and went to looking like this:
>
>http://snapon.lab.bufferbloat.net/~d/beagle_bql/pfifo_bql_tsq3028txqueue1000.svg
>
>And adding the new fq scheduler looked like this:
>
>http://snapon.lab.bufferbloat.net/~d/beagle_bql/fq_bql_tsq3028.svg
>
>(fq_codel was similar)
>
>The fact that we don't achieve full upload throughput on this last
>test is probably
>due to having a tail dropping switch in the way, and/or some dma
>dequeuing
>cleanup conflicts between the low level transmit and receive queues on
>this device (they share an interrupt AND use napi which seems
>puzzling).
>
>But any day I can get a 4-10x improvement in latency and throughput is
>a good day. One IoT device down, thousands to go. It would be nice if
>the chipmakers were incorporating bql into boxes destined for the
>internet of things.
>
>-- 
>Dave Täht
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>Cerowrt-devel mailing list
>Cerowrt-devel at lists.bufferbloat.net
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-- Sent from my Android device with K-@ Mail. Please excuse my brevity.
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