linux-kernel - Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others)

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Date:	Thu, 18 Sep 2008 19:52:16 -0700
From:	"Steven Noonan" <steven@...inklabs.net>
To:	"Luis R. Rodriguez" <lrodriguez@...eros.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"ath9k-devel@...ts.ath9k.org" <ath9k-devel@...ts.ath9k.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Luis Rodriguez" <Luis.Rodriguez@...eros.com>
Subject: Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others)

This IRQ debugging is lots of fun. My /var/log/messages jumped in size
to 241MB. :)

My test case was a file transfer that basically copies 50MB from a
remote machine's /dev/urandom and writes it to /dev/null locally. That
should be a pretty nice large RX. And jeez, I'm seeing tremendous
download speeds now and I have no idea what is different about my
configuration. I'm getting up to 24 megabit per second transfer rates
(actual), which is incredibly unusual for ath9k.

I wasn't able to reproduce the IRQ problems on -tip or Linus' current
tree (both with the group rekeying fix applied, which may or may not
be a good idea for reproducing the issue). Even tried doing
rmmod/modprobe in fast succession multiple times. Couldn't get it to
throw up.

I wonder... My rmmod/modprobe originally was used after the improper
group rekeying before in order to get it back to normal. Perhaps the
encryption has to go wonky before this IRQ issue surfaces? Another
possibility is the earlier mentioned "ACPI: EC: GPE storm detected,
disabling EC GPE". I don't know if it's related or not, but I haven't
waited for it to show up before testing.

Oh well, if the IRQ problem resurfaces (or if I get a ridiculous
latency tomorrow morning with irqpoll off), I'll try to get some
useful data to help debug it.
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