To: linux-wireless@vger.kernel.org
From: Julian Sikorski <belegdol@gmail.com>
Subject: Re: Low 5 GHz performance of Intel Advanced-N 6230
Date: Thu, 24 Apr 2014 18:24:00 +0200
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W dniu 24.04.2014 08:10, Julian Sikorski pisze:
> Dear all,
> 
> I have been moderately recently hit by a performance drop of Intel
> Advanced-N 6230 card. I unfortunately do not have the "before" numbers,
> but I have noticed this since I was able to stream bluray rips over nfs
> to a wired Raspberry Pi a while ago and now I cannot. This has lead me
> to begin investigating the issue.
> In the end I have used iperf3, testing speeds between RPi and laptop,
> with laptop running both Windows and Linux. iperf3 on RPi was always the
> same, on the laptop it was self-compiled iperf3 git master (on Windows I
> used Cygwin). Please see the observed speeds below:
> - Windows: upload to RPi 93 Mbit/s, download from RPi 54 Mbit/s
> - Fedora: upload to RPi 26 Mbit/s, download from RPi 48 Mbit/s
> 
> This is all on Fedora 20 x86_64. Please find attached the journalctl log
> for the last boot. Please let me know if more information is needed - I
> would love to get my network speeds back up to the level where I can
> watch bluray rips again. Thank you for your support in advance.
> 
> Best regards,
> Julian
> 
Hello again,

I have narrowed this down to have regressed between 3.13.6-200.fc20 and
3.13.7-200. Using pointers from Josh Boyer of #fedora-devel, I have
managed to restore the previous performance by loading iwlwifi with
11n_disable=8. I am now at 3.14.1-200 with that option enabled and the
network is fast as it used to be.
Is such a major performance hit expected from this change? Here is the
commit in question:
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-3.13.y&id=45e5cb4f43d33e72ff5f98c80b081eb42e4e4182

Best regards,
Julian