Throttling GPU usage

[wbruna]

On my aging 3400G, the whole desktop GUI (Linux, either X11+XFCE or Wayland+KDE) tends to freeze completely during llama.cpp/stable-diffusion.cpp more intensive GPU computations (on Vulkan). From low to high impact:

• low-ish (<= 256-512, depending on the model) batch processing with no layer offloading runs fine, even hitting >95% GPU usage;
• higher batch processing causes some GUI stuttering, and tends to slow down prompt processing speed;
• full offloading makes the GUI unusable, freezing for 2-3 seconds at a time, mainly during prompt processing;
• stable-diffusion.cpp inference also causes 2-3 second freezes;
• stable-diffusion.cpp VAE phase completely freezes the interface during its whole run (20s-120s, depending on image size)

Also, these 'choking' events sometimes trigger driver bugs, causing full system lock-ups.

So, I'm looking for ways to throttle GPU usage during inference. What I tried so far:

• operating system utilities: no luck on that front. There seems to be no GPU support in cgroups, and utilities that limit GPU usage seem to always focus on fps or vsync;
• creating the queues with VK_QUEUE_GLOBAL_PRIORITY_LOW_EXT: doesn't seem to have any effect, but I'm not sure if I'm implementing it correctly (I have zero graphics programming experience). Something like this:

      /* static vk_device ggml_vk_get_device(size_t idx) */
      if (strcmp("VK_EXT_global_priority", properties.extensionName) == 0)
          global_priority = true;
      (...)
      VkDeviceQueueGlobalPriorityCreateInfoEXT low_prio = {};
      low_prio.sType = VK_STRUCTURE_TYPE_DEVICE_QUEUE_GLOBAL_PRIORITY_CREATE_INFO_EXT;
      low_prio.globalPriority = VK_QUEUE_GLOBAL_PRIORITY_LOW_EXT;
      if (global_priority) {
          device_queue_create_infos[0].pNext = &low_prio;
      }
  

• sprinkling ctx->device->device.waitIdle() + sleep before ggml_vk_build_graph calls: kind of works as a proof-of-concept thing, but of course is no real solution.

Thoughts?

[wbruna]

It turns out the main culprit was the 'enforce_isolation' option on kernel 6.12. Turning it off eliminates most of the lagging, although I still get some stuttering on VAE processing and at the very beginning of prompt processing.