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I just recently upgraded from 14.04 to 14.10 and immediately started having issues with the wifi on my Dell XPS 13 laptop. It'll work fine for a while (something like 30 min to an hour?) but then the connection starts to go slow (packet loss 25% to 75%) and then it eventually stops. Sometimes it comes back on its own but most times I have to toggle the hardware wifi button (fn + F2).

When filtering logged messages for iwlwifi, seeing a possible error message fail to flush all tx fifo queues Q 0 and multiple messages for Q 4 is inactive and mapped to fifo 0 ra_tid:

$ dmesg | grep iwl
[ 9802.709772] iwlwifi 0000:02:00.0: fail to flush all tx fifo queues Q 0
[ 9802.709778] iwlwifi 0000:02:00.0: Current SW read_ptr 81 write_ptr 84
[ 9802.709813] iwl data: 00000000: 00 00 0e 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
[ 9802.709835] iwlwifi 0000:02:00.0: FH TRBs(0) = 0x80003052
[ 9802.709856] iwlwifi 0000:02:00.0: FH TRBs(1) = 0x801020a1
[ 9802.709868] iwlwifi 0000:02:00.0: FH TRBs(2) = 0x00000000
[ 9802.709881] iwlwifi 0000:02:00.0: FH TRBs(3) = 0x80300053
[ 9802.709893] iwlwifi 0000:02:00.0: FH TRBs(4) = 0x00000000
[ 9802.709907] iwlwifi 0000:02:00.0: FH TRBs(5) = 0x00000000
[ 9802.709921] iwlwifi 0000:02:00.0: FH TRBs(6) = 0x00000000
[ 9802.709933] iwlwifi 0000:02:00.0: FH TRBs(7) = 0x007090ef
[ 9802.709982] iwlwifi 0000:02:00.0: Q 0 is active and mapped to fifo 3 ra_tid 0x0000 [81,84]
[ 9802.710031] iwlwifi 0000:02:00.0: Q 1 is active and mapped to fifo 2 ra_tid 0x0000 [0,0]
[ 9802.710080] iwlwifi 0000:02:00.0: Q 2 is active and mapped to fifo 1 ra_tid 0x0000 [146,199]
[ 9802.710128] iwlwifi 0000:02:00.0: Q 3 is active and mapped to fifo 0 ra_tid 0x0000 [83,83]
[ 9802.710177] iwlwifi 0000:02:00.0: Q 4 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710226] iwlwifi 0000:02:00.0: Q 5 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710274] iwlwifi 0000:02:00.0: Q 6 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710323] iwlwifi 0000:02:00.0: Q 7 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710371] iwlwifi 0000:02:00.0: Q 8 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710420] iwlwifi 0000:02:00.0: Q 9 is active and mapped to fifo 7 ra_tid 0x0000 [240,240]
[ 9802.710469] iwlwifi 0000:02:00.0: Q 10 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710517] iwlwifi 0000:02:00.0: Q 11 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710566] iwlwifi 0000:02:00.0: Q 12 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710614] iwlwifi 0000:02:00.0: Q 13 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710663] iwlwifi 0000:02:00.0: Q 14 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710712] iwlwifi 0000:02:00.0: Q 15 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710761] iwlwifi 0000:02:00.0: Q 16 is inactive and mapped to fifo 1 ra_tid 0x0000 [63,63]
[ 9802.710809] iwlwifi 0000:02:00.0: Q 17 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710858] iwlwifi 0000:02:00.0: Q 18 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]
[ 9802.710906] iwlwifi 0000:02:00.0: Q 19 is inactive and mapped to fifo 0 ra_tid 0x0000 [0,0]

Some more info about my machine:

$ uname -a
Linux 3.16.0-25-generic #33-Ubuntu SMP Tue Nov 4 12:06:54 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ uname -r
3.16.0-25-generic

$ lspci -nn | grep 0280
02:00.0 Network controller [0280]: Intel Corporation Wireless 7260 [8086:08b1] (rev 6b)

Not sure why having these issues now (Never had problems in the past when doing any release upgrades particularly with wifi)

Perhaps it thinks the laptop is idle/standby when it's not? I confirmed that the Power Management setting is off.

Not certain but seems to happen more frequently when using VPN.

Any thoughts? Suggestions?

1

It seems a patch has been made to the kernel 3.16 to fix this wifi issue:

Bug 56581 - iwlwifi iwldvm fail to flush Tx queue

and is also being tracked as/linked to an Ubuntu bug:

iwlwifi 0000:01:00.0: fail to flush all tx fifo queues Q 2

but as of 11/11/2014 has not been yet been released as part of an Ubuntu update:

Seth Forshee (sforshee) wrote on 2014-11-11: #14

The patch hasn't made it through to the released Ubuntu kernels yet. I'll check on the status and try to accelerate the process if needed, but it always takes several weeks for updates to get released due to the amount of regression testing new kernels are subjected to before they are released.

but it's planned to be

Seth Forshee (sforshee) wrote on 2014-11-11: #17

I checked, and the patch is already queued for both trusty and utopic in the next SRU cycle. This means that it won't be in the next kernel update, but the one after that. The next update is already undergoing regression testing so it is too late to get it in for the next kernel update.

Unfortunately, I had to re-install the previous version of Ubuntu 14.04 LTS (from 14.10) on my machine which resolved the issue with the wifi back to working as expected. I plan to hold off upgrading until this bug has been fixed and released.

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