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

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Message-ID: <f488382f0809230022v582df76esa8df8c747ab600df@mail.gmail.com>
Date:	Tue, 23 Sep 2008 00:22:47 -0700
From:	"Steven Noonan" <steven@...inklabs.net>
To:	"Luis R. Rodriguez" <lrodriguez@...eros.com>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Senthilkumar Balasubramanian" 
	<Senthilkumar.Balasubramanian@...eros.com>,
	"ath9k-devel@...ts.ath9k.org" <ath9k-devel@...ts.ath9k.org>,
	"Luis Rodriguez" <Luis.Rodriguez@...eros.com>,
	"Johannes Berg" <johannes@...solutions.net>,
	"Ingo Molnar" <mingo@...e.hu>
Subject: Re: [ath9k-devel] ath9k: massive unexplained latency in 2.6.27 (rc5, rc6, probably others)

On Mon, Sep 22, 2008 at 9:01 AM, Luis R. Rodriguez
<lrodriguez@...eros.com> wrote:
> On Mon, Sep 22, 2008 at 8:11 AM, Steven Noonan <steven@...inklabs.net> wrote:
>> On Mon, Sep 22, 2008 at 1:06 AM, Luis R. Rodriguez
>> <lrodriguez@...eros.com> wrote:
>>> Please test the following patch.
>>>
>>> diff --git a/drivers/net/wireless/ath9k/core.c b/drivers/net/wireless/ath9k/core.c
>>> index c262ef2..9a51739 100644
>>> --- a/drivers/net/wireless/ath9k/core.c
>>> +++ b/drivers/net/wireless/ath9k/core.c
>>> @@ -681,10 +681,12 @@ int ath_open(struct ath_softc *sc, struct ath9k_channel *initial_chan)
>>>         * Enable MIB interrupts when there are hardware phy counters.
>>>         * Note we only do this (at the moment) for station mode.
>>>         */
>>> +#if 0
>>>        if (ath9k_hw_phycounters(ah) &&
>>>            ((sc->sc_ah->ah_opmode == ATH9K_M_STA) ||
>>>             (sc->sc_ah->ah_opmode == ATH9K_M_IBSS)))
>>>                sc->sc_imask |= ATH9K_INT_MIB;
>>> +#endif
>>>        /*
>>>         * Some hardware processes the TIM IE and fires an
>>>         * interrupt when the TIM bit is set.  For hardware
>>>
>>
>> It didn't apply to -rc7, but I managed to apply it manually
>> (apparently you made this for wireless-testing?) and added the #if 0.
>> After 7 hours uptime with the driver, no apparent interrupt storm.
>>
>> I'll do more thorough testing later, but I have a 3 hour drive today,
>> and some packing to do, so it'll need to wait a bit.
>
> Yeah I did it for wireless-testing. Good to hear this so far has
> solved the issue. I'll port it to 27 and post it once I get your
> blessings that this fixed it by a Tested-by.
>

Okay. I'm in Seattle now.

Yes, it solved the issue, but surely an #if 0 isn't a proper solution.
What's the actual bug here? I'm afraid the meaning of what's going on
here isn't exactly intuitive.

Also, I'm doing an 8 hour run with this patch tonight. Maybe more,
depends on when I wake up. ;)

I think if this resolves the issue on two separate ≈8 hour runs, it
should be considered the solution to the issue, unless it resurfaces.

- Steven