Re: [Regression] rt2800usb - Wifi performance issues and connection drops

[Thomas Mann]

On Thu, 9 Mar 2023 18:00:04 +0100
Alexander Wetzel <alexander@xxxxxxxxxxxxxx> wrote:

> On 07.03.23 21:54, Alexander Wetzel wrote:
> >>>  
> >>
> >> 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.  
> 
> Best shot I have so far is a driver bug/issue now exposed by the
> changed traffic pattern from mac80211. And while digging into the
> rt2800usb driver I found a watchdog introduced here:
> https://lore.kernel.org/20190615100100.29800-1-sgruszka@xxxxxxxxxx
> 
>  From mac80211 debugging it looks like it may just be that: A random 
> hang of the driver/card.
> 
> For sure rt2800usb tells mac80211 to stop TXing and needs ages (>30s
> in known sample) to unblock the queue. And this watchdog is disabled
> by default.
> 
> Now I'm clearly wondering, if the changed traffic pattern due to the 
> mac80211 patch is just triggering the random hangs...
> 
> I've also uploaded more test patches to bugzilla.
> 
> @Thomas
> Can you also try with this watchdog enabled? It must be enabled for 
> rt2800lib. Since you have compiled in the driver the following boot 
> parameter should enable it:
>   rt2800lib.watchdog=1

i responded on the bugtracker. Enabling the watchdog doesn't solve the
problem.

> 
> @Stanislaw
> Can you maybe also have a look at the issue and how that looks
> compared to the known random hangs you introduced the watchdog for?
> 
> > 
> > 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@Perry.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'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  
>