Date:   Wed, 8 Mar 2023 08:13:32 +0100
From:   Alexander Wetzel <alexander@...zel-home.de>
To:     Thomas Mann <rauchwolke@....net>
Cc:     Linux regressions mailing list <regressions@...ts.linux.dev>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Helmut Schaa <helmut.schaa@...glemail.com>,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [Regression] rt2800usb - Wifi performance issues and connection
 drops

On 07.03.23 23:31, Thomas Mann wrote:
> Hi Alexander,

Since I suspect we'll exchange quite some mails here:
Top posting is being frowned on the mailing lists on copy.
Details here: https://www.infradead.org/~dwmw2/email.html

I've moved your post to the correct position and replied there.

> 
>>>>
>>>
>>> I just uploaded a test patch to bugzilla.
>>> Please have a look if that fixes the issue.
>>>
>>> If not I would be interested in the output of your iTXQ status.
>>> Enable CONFIG_MAC80211_DEBUGFS and run this command when the
>>> connection is bad and send/share/upload to bugzilla the resulting
>>> debug.out:
>>>
>>> k=1; while [ $k -lt 10 ]; do \
>>> cat /sys/kernel/debug/ieee80211/phy?/netdev:*/stations/*/aqm; \
>>> k=$(($k+1)); done >> debug.out
>>
>> Thomas and I continued with some debugging in
>> https://bugzilla.kernel.org/show_bug.cgi?id=217119
>>
>> But the results so far are unexpected and we decided to continue the
>> debugging with the round here. Hoping someone sees something I miss.
>>
>> A very summary where we are:
>> I can't reproduce the bug with a very similar card and kernel config
>> so far. Thomas card stops the iTXQs for intervalls >30s. Mine
>> operates normally.
>>
>> A more useful but longer summary:
>>
>> Thomas updated to a 6.2 kernel and reported "connection drops and
>> bandwidth problems" with his rt2800usb wlan card. (6.1 is ok.) Asked
>> for some more details he reported:
>> "...slow bandwidth stuff works better, but the main problem/test case
>> is to start a 8-16 mbit video stream, which sometimes runs for a few
>> seconds and then stops or it doesn't start at all"
>>
>> He bisected the issue and identified my commit 4444bc2116ae ("wifi:
>> mac80211: Proper mark iTXQs for resumption") as culprit.
>>
>> Checking the internal iTXQ status when the issue is ongoing shows,
>> that TID zero is flagged as dirty and thus is not transmitting queued
>> packets. Interesting line from
>> /sys/kernel/debug/ieee80211/phy?/netdev:*/stations/*/aqm:
>> tid ac backlog-bytes backlog-packets new-flows drops marks overlimit
>> collisions tx-bytes tx-packets flags
>> 0 2 619736 404 1681 0 0 0 1 4513965 3019 0xe(RUN AMPDU NO-AMSDU DIRTY)
>>
>> --> The "normal" iTXQ handling IEEE80211_AC_BE has queued packets and
>> is flagged as DIRTY. There even is a potential race setting the DIRTY
>> flag, but the fix for that is not helping.
>>
>> Thus Thomas applied two debug patches, to better understand why the
>> DIRTY flag is not cleared.
>>
>> And looking at the output from those we see that the driver stops Tx
>> by calling ieee80211_stop_queue(). When ieee80211_wake_queue()
>> mac80211 correctly resumes TX but is getting stopped by the driver
>> after a single packet again. (The start of the relevant log is
>> missing, so that may be initially more).
>> I assume TX is still ok at that stage. But after some singe Tx
>> operations the driver stops the queues again. Here the relevant part
>> of the log:
>> [  179.584997] XXXX __ieee80211_wake_txqs: waking TID 0
>> [  179.585022] XXXX drv_tx: TX
>> [  179.585027] XXXX ieee80211_stop_queue: called
>> [  179.585028] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.585030] XXXX __ieee80211_wake_txqs: TID 3 NOT dirty
>> [  179.585031] XXXX __ieee80211_wake_txqs: TID 8 NOT dirty
>> [  179.585033] XXXX __ieee80211_wake_txqs: TID 11 NOT dirty
>> [  179.585034] XXXX __ieee80211_wake_txqs: EXIT
>> [  179.585035] XXXX __ieee80211_wake_txqs: ENTRY
>> [  179.585036] XXXX __ieee80211_wake_txqs: TID 1 NOT dirty
>> [  179.585037] XXXX __ieee80211_wake_txqs: TID 2 NOT dirty
>> [  179.585038] XXXX __ieee80211_wake_txqs: TID 9 NOT dirty
>> [  179.585040] XXXX __ieee80211_wake_txqs: TID 10 NOT dirty
>> [  179.585041] XXXX __ieee80211_wake_txqs: EXIT
>> [  179.585047] XXXX drv_tx: TX
>> [  179.585056] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.585271] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.585868] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.586120] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.586544] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.586792] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.587317] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.587591] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> [  179.588569] XXXX ieee80211_tx_dequeue: mark TID 0 dirty. Reason: 1
>> ....
>> [  214.307617] XXXX ieee80211_wake_queue: called
>>
>>
>> --> So the driver blocked TX for more than 30s. Which is a good
>> explanation of what Thomas observes.
>>
>> But there is nothing mac80211 can do differently here. Whatever is
>> the real reason for the issue, it's nothing obvious I see.
>>
>> Luckily I found a card using the same driver and nearly the same card:
>> Thomas systems:Linux version 6.2.2-gentoo (root@foo) (gcc (Gentoo
>> Hardened 12.2.1_p20230121-r1 p10) 12.2.1 20230121, GNU ld (Gentoo
>> 2.39 p5) 2.39.0) #2 SMP Fri Mar  3 16:59:02 CET 2023ieee80211 phy0:
>> rt2x00_set_rt: Info - RT chipset 3070, rev 0201 detected
>> ieee80211 phy0: rt2x00_set_rf: Info - RF chipset 0005 detected
>> ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
>>
>> My system, using the kernel config from Thomas with only minor
>> modifications (different filesystems and initramfs settings and
>> enabled mac80211 debug and developer options):
>> Linux version 6.2.2-gentoo (root@...ry.mordor) (gcc (Gentoo
>> 12.2.1_p20230121-r1 p10) 12.2.1 20230121, GNU ld (Gentoo 2.40 p2)
>> 2.40.0) #2 SMP Tue Mar  7 18:18:47 CET 2023ieee80211 phy0:
>> rt2x00_set_rt: Info - RT chipset 3070, rev 0200 detected
>> ieee80211 phy0: rt2x00_set_rf: Info - RF chipset 0005 detected
>> ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
>> ieee80211 phy0: rt2x00lib_request_firmware: Info - Loading firmware
>> file 'rt2870.bin'
>> ieee80211 phy0: rt2x00lib_request_firmware: Info - Firmware detected
>> - version: 0.36
>>
>> But there is one big difference on my system: I can't reproduce the
>> bug so far. It's working as it should... (I did not apply the debug
>> patches myself so far)
>>
>> I'm now planning to look a bit more into the rt2800usb driver and
>> provide another debug patch for interesting looking code pieces in it.
>>
>> @Thomas:
>> I've also uploaded you my binary kernel I'm running at the moment
>> here: https://www.awhome.eu/s/5FjqMS73rtCtSBM
>>
>> That kernel should also be able to boot and operate your system. Can
>> you try that and tell me, if that makes any difference?

 >
 > i can't boot the binary kernel here, as the initramfs is included in
 > my kernel, if you send me a patch, i can apply it and test it.

That was an unpatched kernel. Idea was to verify that it's not a 
compiler issue. (You seem to be using a hardened Gentoo profile.)

Can you share your initrd, so I can include it? (Mail it to me directly, 
upload it to bug in buguilla or send a link to some cloud storage.)



>>
>> I'm also planning to provide some more debug patches, to figuring out
>> which part of commit 4444bc2116ae ("wifi: mac80211: Proper mark iTXQs
>> for resumption") fixes the issue for you. Assuming my understanding
>> above is correct the patch should not really fix/break anything for
>> you...With the findings above I would have expected your git bisec to
>> identify commit a790cc3a4fad ("wifi: mac80211: add wake_tx_queue
>> callback to drivers") as the first broken commit...
>>
>> Alexander
> 

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