Public bug reported:

After updating to the latest kernel 5.0.0-15 I'm experiencing a severe
performance degradation on my machine with one of my applications (a gbc
emulator developed by me).

I saw about a 27% performance loss, going from 55fps to 40.

Booting an old 5.0.0-13 kernel or disabling mds mitigation at boot with
'mds=off' solves the problem.

I know there isn't much to do about (apart from disabling the mitigation) but 
I'm reporting this
because I spent half a day bisecting with git cause I thought the problem was 
with my latest commits.

Security updates are obviously important and a priority, but I think that at 
least with this kind
of mitigations that cause big performance degradation, an message or a simple 
alert to the user
during the update should be shown. Something like: "Plese be aware that this 
kernel update can 
result in performance loss. See this page for more info." and then link the 
specific SecurityTeam
page (which in this case is )

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: linux-image-5.0.0-15-generic 5.0.0-15.16
ProcVersionSignature: Ubuntu 5.0.0-15.16-generic 5.0.6
Uname: Linux 5.0.0-15-generic x86_64
ApportVersion: 2.20.10-0ubuntu27
Architecture: amd64
 /dev/snd/controlC0:  gabriele   2045 F.... pulseaudio
 /dev/snd/controlC1:  gabriele   2045 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Wed May 15 16:36:36 2019
HibernationDevice: RESUME=UUID=e43b75a3-a278-4d4e-83e8-54a9e0c95276
InstallationDate: Installed on 2018-05-31 (349 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
MachineType: Dell Inc. Latitude E6540
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.0.0-15-generic 
root=UUID=8a8a023d-2a12-4e14-b187-7beaf4d89763 ro quiet splash vt.handoff=1
 linux-restricted-modules-5.0.0-15-generic N/A
 linux-backports-modules-5.0.0-15-generic  N/A
 linux-firmware                            1.178
SourcePackage: linux
UpgradeStatus: Upgraded to disco on 2019-04-23 (21 days ago) 10/09/2018
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A26 0725FP
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi:bvnDellInc.:bvrA26:bd10/09/2018:svnDellInc.:pnLatitudeE6540:pvr00:rvnDellInc.:rn0725FP:rvrA00:cvnDellInc.:ct9:cvr: Latitude E6540
dmi.product.sku: 05BE
dmi.product.version: 00
dmi.sys.vendor: Dell Inc.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Confirmed

** Tags: amd64 apport-bug disco

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  Sever performance degradation after updating to 5.0.0-15 due to mds

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