The rather large negative deficit stands out to me. See this patch, https://patchwork.kernel.org/patch/11246363/ specifically the comments by Kan Yan On Thu, Jan 2, 2020, 3:14 PM Stephen Oberholtzer <stevie@xxxxxxxxx> wrote: > > > /sys/kernel/debug/ieee80211/phy0 > > airtime_flags = 7 > > stations/<my AP's MAC>/airtime = > > RX: 6583578 us > TX: 32719 us > Weight: 256 > Deficit: VO: -1128 us VI: 11 us BE: -5098636 us BK: 256 us > Q depth: VO: 3868 us VI: 3636 us BE: 12284 us BK: 0 us > Q limit[low/high]: VO: 5000/12000 VI: 5000/12000 BE: 5000/12000 BK: 5000/1200 On Thu, Jan 2, 2020 at 3:14 PM Stephen Oberholtzer <stevie@xxxxxxxxx> wrote: > > On Thu, Jan 2, 2020 at 8:28 AM Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: > > > > On Tue, 2019-12-31 at 19:49 -0500, Stephen Oberholtzer wrote: > > > Wireless networking goes down on Acer C720P Chromebook (bisected) > > > > > > Culprit: 7a89233a ("mac80211: Use Airtime-based Queue Limits (AQL) on > > > packet dequeue") > > > > > <snip> > > > I think I found at least one hole in this, but IIRC (it was before my > > vacation, sorry) it was pretty unlikely to actually happen. Perhaps > > there are more though. > > > > https://lore.kernel.org/r/b14519e81b6d2335bd0cb7dcf074f0d1a4eec707.camel@xxxxxxxxxxxxxxxx > > <snippety-snip> > > > Do you get any output at all? Like a WARN_ON() for an underflow, or > > something? > > > > johannes > > > > Johannes, > > To answer your immediate question, no, I don't get any dmesg output at > all. Nothing about underruns. > However, while pursuing other avenues -- specifically, enabling > mac80211 debugfs and log messages -- I realized that my 'master' was > out-of-date from linux-stable and did a git pull. Imagine my surprise > when the resulting kernel did not exhibit the problem! > > Apparently, I had been a bit too pessimistic; since the problem > existed in 5.5-rc1 release, I'd assumed that the problem wouldn't get > rectified before 5.5. > > However, I decided to bisect the fix, and ended up with: 911bde0f > ("mac80211: Turn AQL into an NL80211_EXT_FEATURE"), which appears to > have "solved" the problem by just disabling the feature (this is > ath9k, by the way.) > > This AQL stuff sounds pretty nifty, and I'd love to try my hand at > making it work for ath9k (also, since I put so much effort into an > automated build-and-test framework, it'd be a shame to just abandon > it.) However, the ath9k code is rather lacking for comments, so I > don't even know where I should start, except for (I suspect) a call to > `wiphy_ext_feature_set(whatever, NL80211_EXT_FEATURE_AQL);` from > inside ath9k_set_hw_capab()? > > In the meantime, I went back to e548f749b096 -- the commit prior to > the one making AQL support opt-in -- and cranked up the debugging. > > I'm not sure how to interpret any of this, but here's what I got: > > dmesg output: > > Last relevant mention is "moving STA <my AP's MAC> to state 4" which > happened during startup, before everything shut down. > > /sys/kernel/debug/ieee80211/phy0 > > airtime_flags = 7 > > stations/<my AP's MAC>/airtime = > > RX: 6583578 us > TX: 32719 us > Weight: 256 > Deficit: VO: -1128 us VI: 11 us BE: -5098636 us BK: 256 us > Q depth: VO: 3868 us VI: 3636 us BE: 12284 us BK: 0 us > Q limit[low/high]: VO: 5000/12000 VI: 5000/12000 BE: 5000/12000 BK: 5000/12000 > > (I have no idea how to interpret this, but that '32719 us' seems odd, > I thought the airtime usage was in 4us units?) > > > Doing an 'echo 3 | tee airtime_flags' to clear the (old) AQL-enabled > bit seemed to *immediately* restore network connectivity. > > I ran a ping, and saw this: > > - pings coming back in <5ms > - re-enable AQL (echo 7 | tee airtime_flags) > - pings stop coming back immediately > - some seconds later, disable AQL again (echo 3 | tee airtime_flags) > - immediate *flood* of ping replies registered, with times 16000ms, > 15000ms, 14000ms, .. down to 1000ms, 15ms, then stabilizing sub-5ms > - According to the icmp_seq values, all 28 requests were replied to, > and their replies were delivered in-order > > This certainly looks like a missing TX queue restart to me? > > > -- > -- Stevie-O > Real programmers use COPY CON PROGRAM.EXE
