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

[Alexander Wetzel]

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@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 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