Corsair M95 Gaming Mouse too sensitive / speed too fast. How to reduce speed?

Question

The mouse control panel window slider does nothing. The official thread does not seem to affect this particular mouse due to it's xinput props being different: Reduce the Mouse Sensitivity

Here's what I've tried:

xinput set-prop 9 "libinput Accel Speed Default" 2.88

X Error of failed request:  BadAccess (attempt to access private resource denied)
  Major opcode of failed request:  131 (XInputExtension)
  Minor opcode of failed request:  57 ()
  Serial number of failed request:  20
  Current serial number in output stream:  21

And:

xinput set-prop $MOUSE_ID "Device Accel Constant Deceleration" 2.88 

property 'Device Accel Constant Deceleration' doesn't exist, you need to specify its type and format

Here are the props:

xinput list-props 9        
Device 'Corsair Corsair M95 Gaming Mouse':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    libinput Accel Speed (287): 0.000000
    libinput Accel Speed Default (288): 0.000000
    libinput Accel Profiles Available (289):    1, 1
    libinput Accel Profile Enabled (290):   1, 0
    libinput Accel Profile Enabled Default (291):   1, 0
    libinput Natural Scrolling Enabled (292):   0
    libinput Natural Scrolling Enabled Default (293):   0
    libinput Send Events Modes Available (272): 1, 0
    libinput Send Events Mode Enabled (273):    0, 0
    libinput Send Events Mode Enabled Default (274):    0, 0
    libinput Left Handed Enabled (294): 0
    libinput Left Handed Enabled Default (295): 0
    libinput Scroll Methods Available (296):    0, 0, 1
    libinput Scroll Method Enabled (297):   0, 0, 0
    libinput Scroll Method Enabled Default (298):   0, 0, 0
    libinput Button Scrolling Button (299): 2
    libinput Button Scrolling Button Default (300): 2
    libinput Middle Emulation Enabled (301):    0
    libinput Middle Emulation Enabled Default (302):    0
    Device Node (275):  "/dev/input/event2"
    Device Product ID (276):    6940, 6918
    libinput Drag Lock Buttons (303):   <no items>
    libinput Horizontal Scroll Enabled (304):   1



 jonny  ~  xinput list-props 11
Device 'Corsair Corsair M95 Gaming Mouse':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    libinput Natural Scrolling Enabled (292):   0
    libinput Natural Scrolling Enabled Default (293):   0
    libinput Send Events Modes Available (272): 1, 0
    libinput Send Events Mode Enabled (273):    0, 0
    libinput Send Events Mode Enabled Default (274):    0, 0
    Device Node (275):  "/dev/input/event4"
    Device Product ID (276):    6940, 6918
    libinput Drag Lock Buttons (303):   <no items>
    libinput Horizontal Scroll Enabled (304):   1



 jonny  ~  xinput list-props 10
Device 'Corsair Corsair M95 Gaming Mouse':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    libinput Send Events Modes Available (272): 1, 0
    libinput Send Events Mode Enabled (273):    0, 0
    libinput Send Events Mode Enabled Default (274):    0, 0
    Device Node (275):  "/dev/input/event3"
    Device Product ID (276):    6940, 6918


 jonny  ~  xinput list-props 15
Device 'Corsair Corsair M95 Gaming Mouse':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    libinput Natural Scrolling Enabled (292):   0
    libinput Natural Scrolling Enabled Default (293):   0
    libinput Send Events Modes Available (272): 1, 0
    libinput Send Events Mode Enabled (273):    0, 0
    libinput Send Events Mode Enabled Default (274):    0, 0
    Device Node (275):  "/dev/input/event4"
    Device Product ID (276):    6940, 6918

xinput list-props 4
Device 'Virtual core XTEST pointer':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    XTEST Device (271): 1
xinput list-props 2 
Device 'Virtual core pointer':
    Device Enabled (153):   1
    Coordinate Transformation Matrix (155): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000

And:

xinput                                                                                                                                                                                                                       1 
⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ Corsair Corsair M95 Gaming Mouse          id=9    [slave  pointer  (2)]
⎜   ↳ Corsair Corsair M95 Gaming Mouse          id=11   [slave  pointer  (2)]
⎜   ↳ Razer Razer BlackWidow Ultimate           id=13   [slave  pointer  (2)]
⎜   ↳ Razer Razer BlackWidow Ultimate           id=14   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ UVC Camera (046d:0807)                    id=8    [slave  keyboard (3)]
    ↳ Corsair Corsair M95 Gaming Mouse          id=10   [slave  keyboard (3)]
    ↳ Razer Razer BlackWidow Ultimate           id=12   [slave  keyboard (3)]
    ↳ Corsair Corsair M95 Gaming Mouse          id=15   [slave  keyboard (3)]
    ↳ Razer Razer BlackWidow Ultimate           id=16   [slave  keyboard (3)]

Answer 1

I was super close:

xinput set-prop $MOUSE_ID "libinput Accel Speed" -0.9

Where

MOUSE_ID=`xinput list | grep -i Corsair | awk '{print $(NF-3)}' | cut -c4-5 | head -n 1

Per: https://patrickmn.com/aside/lowering-gaming-mouse-sensitivity-in-ubuntu-9-10/

Answer 2

For those who don't have Device Accel Constant Deceleration like me.

The values for libinput Accel Speed can be negative, e.g.

xinput --set-prop 'pointer:Logitech MX Master' 'libinput Accel Speed' -0.5

To find your mouse name: xinput | grep pointer, don't forget to prefix it with pointer: as my mouse shows up as a keyboard too.