lenovo t420s very slow wifi after dist upgrade 14-16

[Aleksei]

it is not more than 2 mbit\s for the moment - before upgrade it works well - about 40-50 mbit\s.
it is not ISP issue other devices works fast at my wifi network

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.16
ProcVersionSignature: Ubuntu 4.4.0-38.57-generic 4.4.19
Uname: Linux 4.4.0-38-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Thu Sep 22 00:29:18 2016
InstallationDate: Installed on 2015-12-17 (279 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: Upgraded to xenial on 2016-08-17 (35 days ago)
VarLogDistupgradeTermlog:

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream stable kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.4 stable kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4.23

[Aleksei (tav-susp)]

now it is about 23 mbit\s, but actually my wifi signal is about 100 mbit\s and my IPAD gets about 80 \ 100 (download\upload). I consider that fix as good but there is a room for an improvement

[Aleksei (tav-susp)]

it is happening again - no idea on how to solve it

[Aleksei (tav-susp)]

As I managed to solve the problem before and after updates I started using latest kernel where the problem reveals again, I put my working config here

First - this one - sudo vim /etc/modprobe.d/iwlwifi-disable11n.conf
having this one inside - options iwlwifi 11n_disable=0
is not affecting the wi-fi speed

Secondly, I've installed 3.19 kernel - and it works for me

GRUB config

1. Using grub-customizer, I've put 3.19 entry on top of menu list, to have it
 being run with just one 'enter' key

2. I've put here - sudo gedit /etc/default/grub
the following - GRUB_DEFAULT="Ubuntu, with Linux 3.19.0-66-generic"

the speed is good - about 36 MBit/second for upload/download both

Hope it will help someone

Note, that the latest (4.4.23 kernel) have buggy slow wi-fi driver(0.5, 2 MBit/second)

[Aleksei (tav-susp)]

sorry - The config above is not working as well. I mean - it is unstable - it may give 35 MBit/s
or 0.5 MBit/s. No relation with '11n_disable' setting found. I tried several kernels - 4.4.10 - but haven't been able to find stable working one - so the question is still open