llama.cpp: thing

services/llama-cpp.nix

@@ -50,17 +50,40 @@ in
       "4096"
       "-ub"
       "4096"
+      "--parallel"
+      "2"
     ];
   };
 
   # have to do this in order to get vulkan to work
   systemd.services.llama-cpp.serviceConfig.DynamicUser = lib.mkForce false;
 
+  # ANV driver's turbo3 shader compilation exceeds the default 8 MB thread stack.
+  systemd.services.llama-cpp.serviceConfig.LimitSTACK = lib.mkForce "67108864"; # 64 MB soft+hard
+
   # llama-server tries to create ~/.cache; ProtectSystem=strict + impermanent
   # root make /root read-only. Give it a writable cache dir and point HOME there.
   systemd.services.llama-cpp.serviceConfig.CacheDirectory = "llama-cpp";
   systemd.services.llama-cpp.environment.HOME = "/var/cache/llama-cpp";
 
+  # turbo3 KV cache quantization runs a 14-barrier WHT butterfly per 128-element
+  # workgroup in SET_ROWS. With 4 concurrent slots and batch=4096, the combined
+  # GPU dispatch can exceed the default i915 CCS engine preempt timeout (7.5s),
+  # causing GPU HANG -> ErrorDeviceLost. Increase compute engine timeouts.
+  # Note: batch<4096 is not viable -- GDN chunked mode needs a larger compute
+  # buffer at smaller batch sizes, exceeding the A380's 6 GB VRAM.
+  # '+' prefix runs as root regardless of service User=.
+  systemd.services.llama-cpp.serviceConfig.ExecStartPre = [
+    "+${pkgs.writeShellScript "set-gpu-compute-timeout" ''
+      for f in /sys/class/drm/card*/engine/ccs*/preempt_timeout_ms; do
+        [ -w "$f" ] && echo 30000 > "$f"
+      done
+      for f in /sys/class/drm/card*/engine/ccs*/heartbeat_interval_ms; do
+        [ -w "$f" ] && echo 10000 > "$f"
+      done
+    ''}"
+  ];
+
   # upstream module hardcodes --log-disable; override ExecStart to keep logs
   # so we can see prompt processing progress via journalctl
   systemd.services.llama-cpp.serviceConfig.ExecStart = lib.mkForce (