netris-nestri/build/patches/mesa/0001-ac-linux_drm-cache-the-device-s-static-VRAM-GTT-size.patch

From 5f615ac88a6f2b962a3e0d68c995f1ab3ec12d20 Mon Sep 17 00:00:00 2001
From: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>
Date: Thu, 17 Sep 2026 19:33:08 +0300
Subject: [PATCH] ac/linux_drm: cache the device's static VRAM/GTT sizes

AMDGPU_INFO_VRAM_GTT returns total VRAM, CPU-visible VRAM and GTT size.
All three are fixed properties of the device and cannot change while it is
open, but ac_drm_query_heap_info() asked for them on every call.

That is free on a local ioctl. It is not free on an amdgpu native context,
where every query is a synchronous round trip to the host: measured with one
game running under virtio, this single query was 47% of all guest-to-host
traffic, asked roughly 15,000 times a second for an answer that never
changed.

Fetch it once during ac_drm_device_initialize(), before the device is
visible to any other thread, so reading it needs no lock. A failure there is
not fatal -- vram_gtt_valid stays false and the old per-call path is used.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 src/amd/common/ac_linux_drm.c | 40 +++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/src/amd/common/ac_linux_drm.c b/src/amd/common/ac_linux_drm.c
index 21fb2c9e4e3..63b27058ec1 100644
--- a/src/amd/common/ac_linux_drm.c
+++ b/src/amd/common/ac_linux_drm.c
@@ -28,6 +28,23 @@ struct ac_drm_device {
    struct util_sync_provider *p;
    int fd;
    bool is_virtio;
+
+   /* AMDGPU_INFO_VRAM_GTT, fetched once.
+    *
+    * The three sizes it returns -- total VRAM, CPU-visible VRAM, GTT -- are
+    * fixed properties of the device and cannot change while it is open, but
+    * ac_drm_query_heap_info() re-queried them on every call. That is free on a
+    * local ioctl and is not free over virtio, where every query is a
+    * synchronous round trip to the host: measured on an amdgpu native context,
+    * this single query was 47% of all guest-to-host traffic, asked ~15,000
+    * times a second for an answer that never changed.
+    *
+    * Filled during initialize(), before the device is visible to any other
+    * thread, so reading it needs no lock. If the query fails there,
+    * vram_gtt_valid stays false and the old per-call path is used.
+    */
+   struct drm_amdgpu_info_vram_gtt vram_gtt;
+   bool vram_gtt_valid;
 };
 
 int ac_drm_device_initialize(int fd, bool is_virtio,
@@ -64,10 +81,17 @@ int ac_drm_device_initialize(int fd, bool is_virtio,
       }
    }
 
-   if (r == 0)
+   if (r == 0) {
       (*dev)->is_virtio = is_virtio;
-   else
+      /* Device-static, so it is asked once here rather than on every heap
+       * query. A failure is not fatal: the caller falls back to querying it.
+       */
+      (*dev)->vram_gtt_valid =
+         ac_drm_query_info(*dev, AMDGPU_INFO_VRAM_GTT, sizeof((*dev)->vram_gtt),
+                           &(*dev)->vram_gtt) == 0;
+   } else {
       free(*dev);
+   }
 
    return r;
 }
@@ -757,12 +781,16 @@ int ac_drm_query_gpu_info(ac_drm_device *dev, struct amdgpu_gpu_info *info)
 int ac_drm_query_heap_info(ac_drm_device *dev, uint32_t heap, uint32_t flags,
                            struct amdgpu_heap_info *info)
 {
-   struct drm_amdgpu_info_vram_gtt vram_gtt_info = {};
+   struct drm_amdgpu_info_vram_gtt vram_gtt_info;
    int r;
 
-   r = ac_drm_query_info(dev, AMDGPU_INFO_VRAM_GTT, sizeof(vram_gtt_info), &vram_gtt_info);
-   if (r)
-      return r;
+   if (dev->vram_gtt_valid) {
+      vram_gtt_info = dev->vram_gtt;
+   } else {
+      r = ac_drm_query_info(dev, AMDGPU_INFO_VRAM_GTT, sizeof(vram_gtt_info), &vram_gtt_info);
+      if (r)
+         return r;
+   }
 
    /* Get heap information */
    switch (heap) {