From: Dave Taht <dave.taht@gmail.com>
To: Felix Fietkau <nbd@nbd.name>, make-wifi-fast@lists.bufferbloat.net
Cc: linux-wireless <linux-wireless@vger.kernel.org>,
"Michal Kazior" <michal.kazior@tieto.com>,
"Toke Høiland-Jørgensen" <toke@toke.dk>
Subject: Re: [Make-wifi-fast] TCP performance regression in mac80211 triggered by the fq code
Date: Tue, 12 Jul 2016 14:13:48 +0200 [thread overview]
Message-ID: <CAA93jw6=_pemSUjk3dje1GmnTzrs+=pEdza4j1Wjtrw+VKNdNg@mail.gmail.com> (raw)
In-Reply-To: <11fa6d16-21e2-2169-8d18-940f6dc11dca@nbd.name>
On Tue, Jul 12, 2016 at 12:09 PM, Felix Fietkau <nbd@nbd.name> wrote:
> Hi,
>
> With Toke's ath9k txq patch I've noticed a pretty nasty performance
> regression when running local iperf on an AP (running the txq stuff) to
> a wireless client.
Your kernel? cpu architecture?
What happens when going through the AP to a server from the wireless client?
Which direction?
> Here's some things that I found:
> - when I use only one TCP stream I get around 90-110 Mbit/s
with how much cpu left over?
> - when running multiple TCP streams, I get only 35-40 Mbit/s total
with how much cpu left over?
context switch difference between the two tests?
tcp_limit_output_bytes is?
got perf?
> - fairness between TCP streams looks completely fine
A codel will get to long term fairness pretty fast. Packet captures
from a fq will show much more regular interleaving of packets,
regardless.
> - there's no big queue buildup, the code never actually drops any packets
A "trick" I have been using to observe codel behavior has been to
enable ecn on server and client, then checking in wireshark for ect(3)
marked packets.
> - if I put a hack in the fq code to force the hash to a constant value
You could also set "flows" to 1 to keep the hash being generated, but
not actually use it.
> (effectively disabling fq without disabling codel), the problem
> disappears and even multiple streams get proper performance.
Meaning you get 90-110Mbits ?
Do you have a "before toke" figure for this platform?
> Please let me know if you have any ideas.
I am in berlin, packing hardware...
>
> - Felix
> --
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--
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org
next parent reply other threads:[~2016-07-12 12:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <11fa6d16-21e2-2169-8d18-940f6dc11dca@nbd.name>
2016-07-12 12:13 ` Dave Taht [this message]
2016-07-12 13:21 ` Felix Fietkau
2016-07-12 14:02 ` Dave Taht
2016-07-13 7:57 ` Dave Taht
2016-07-13 8:53 ` Felix Fietkau
2016-07-13 9:13 ` Dave Taht
2016-07-19 13:10 ` Michal Kazior
[not found] ` <87shvfujl4.fsf@toke.dk>
[not found] ` <CAA93jw6z53P+JCPsjYD-vaY+9vq9ZO-Ob_cXm0AE76uVcM=F9g@mail.gmail.com>
[not found] ` <87bn23ui87.fsf@toke.dk>
2016-07-12 13:03 ` Dave Taht
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