The Linux graphics stack in a nutshell, part 1

Posted Dec 23, 2023 13:52 UTC (Sat) by adobriyan (subscriber, #30858)
In reply to: The Linux graphics stack in a nutshell, part 1 by adobriyan
Parent article: The Linux graphics stack in a nutshell, part 1

OK, this is funny. lavapipe is here, ready to help. Filtering by GPU type is required apparently:

# 1070 (active)
qfp 0 G 1, P 1 ***
qfp 1 G 0, P 0
qfp 2 G 0, P 1
qfp 3 G 0, P 0

# 1030 (passive)
qfp 0 G 1, P 0
qfp 1 G 0, P 0
qfp 2 G 0, P 0
qfp 3 G 0, P 0

(lavapipe)
qfp 0 G 1, P 1 *** # P=1 !!!
-p 0 NVIDIA GeForce GTX 1070
-p 1 NVIDIA GeForce GT 1030
-p 2 llvmpipe (LLVM 16.0.6, 256 bits)

Enumeration order varies by distro too!

The Linux graphics stack in a nutshell, part 1

Posted Feb 2, 2024 8:34 UTC (Fri) by daenzer (subscriber, #7050) [Link]

> Enumeration order varies by distro too!

The enumeration order isn't well-defined, and in practice partially depends on the order in which the filesystem enumerates the corresponding *_icd.*.json files (which isn't well-defined either). So the order may differ between otherwise mostly identical systems with the same set of VkPhysicalDevices, and may change after modifications to the *_icd.*.json files.

Unfortunately, many (most?) Vulkan applications just use the first enumerated device by default. To prevent such apps from accidentally using an undesirable device such as a lavapipe one, Mesa ships a device selection layer which moves the "default" device to be enumerated first.