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From: Felix Fietkau <nbd@nbd.name>
To: Dave Taht <dave.taht@gmail.com>
Cc: make-wifi-fast@lists.bufferbloat.net,
	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: Wed, 13 Jul 2016 08:53:12 -0000	[thread overview]
Message-ID: <cac14ead-1af5-ff1d-5b35-592933882aae@nbd.name> (raw)
In-Reply-To: <CAA93jw7y_dp=AMFB3Nj7TK08PXmdypKBnfAZ_FfnWXOt-+aL2Q@mail.gmail.com>

On 2016-07-13 09:57, Dave Taht wrote:
> On Tue, Jul 12, 2016 at 4:02 PM, Dave Taht <dave.taht@gmail.com> wrote:
>> On Tue, Jul 12, 2016 at 3:21 PM, Felix Fietkau <nbd@nbd.name> wrote:
>>> On 2016-07-12 14:13, Dave Taht wrote:
>>>> 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?
>>> QCA9558, 720 MHz, running Linux 4.4.14
> 
> So this is a single core at the near-bottom end of the range. I guess
> we also should find a MIPS 24c derivative that runs at 400Mhz or so.
> 
> What HZ? (I no longer know how much higher HZ settings make any
> difference, but I'm usually at NOHZ and 250, rather than 100.)
> 
> And all the testing to date was on much higher end multi-cores.
> 
>>>> What happens when going through the AP to a server from the wireless client?
>>> Will test that next.
> 
> Anddddd?
Single stream: 130 Mbit/s, 70% idle
Two streams: 50-80 Mbit/s (wildly fluctuating), 73% idle.

>>>> Which direction?
>>> AP->STA, iperf running on the AP. Client is a regular MacBook Pro
>>> (Broadcom).
>>
>> There are always 2 wifi chips in play. Like the Sith.
>>
>>>>> 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?
>>> ~20%
>>>
>>>>> - when running multiple TCP streams, I get only 35-40 Mbit/s total
>>>> with how much cpu left over?
>>> ~30%
> 
> To me this implies a contending lock issue, too much work in the irq
> handler or too delayed work in the softirq handler....
> 
> I thought you were very brave to try and backport this.
I don't think this has anything to do with contending locks, CPU
utilization, etc. The code does something to the packets that TCP really
doesn't like.

- Felix

  reply	other threads:[~2016-07-13  8:53 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
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 [this message]
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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