Kan Yan <kyan@xxxxxxxxxx> writes:
>> In theory, this ought to produce a histogram of sojourn times (in
>> microseconds):
>> bpftrace -e 'kretprobe:codel_skb_time_func { @sojourn = lhist((nsecs -
> (retval << 10))/1000, 0, 100000, 1000); }'
>
> Thanks for the tips!
>
>> Can't get the CoDel drop mechanism to trigger on my system at all,
>> though (a laptop running on iwl). I guess because there's queue
>> backpressure to userspace first?
>
> What's the tcp_congestion_control in your system? Maybe it is BBR that
> prevents bufferbloat.
It's not BBR, just plain old CUBIC. I've seen the issue before that it's
almost impossible to build a queue in the mac80211 layer when the TCP
session is originated on the local machine, though...
>> It would be interesting to see if it works for you, assuming you can get
>> bpftrace to work on your test system :)
>
> I can enable required kernel configuration easily, but cross-compile
> bpftrace for an ARM64 platform may take some time and effort.
Yeah, bpftrace can be a bit of a pain to get running; but it may be
worth the investment longer term as well. It really is quite useful! :)
Some links:
Install guide:
https://github.com/iovisor/bpftrace/blob/master/INSTALL.md
Tutorial by one-liners:
https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md
Reference guide:
https://github.com/iovisor/bpftrace/blob/master/docs/reference_guide.md#5-tracepoint-static-tracing-kernel-level
-Toke
