drm/amdgpu: move devcoredump generation to a worker

Update the way drm_coredump_printer is used based on its documentation
and Xe's code: the main idea is to generate the final version in one go
and then use memcpy to return the chunks requested by the caller of
amdgpu_devcoredump_read.

The generation is moved to a separate worker thread.

This cuts the time to copy the dump from 40s to ~0s on my machine.

---
v3:
- removed adev->coredump_in_progress and instead use work as
  the synchronisation mechanism
- use kvfree instead of kfree
---

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -327,6 +327,7 @@ struct kfd_vm_fault_info;
 struct amdgpu_hive_info;
 struct amdgpu_reset_context;
 struct amdgpu_reset_control;
+struct amdgpu_coredump_info;
 
 enum amdgpu_cp_irq {
 	AMDGPU_CP_IRQ_GFX_ME0_PIPE0_EOP = 0,
@@ -1147,6 +1148,11 @@ struct amdgpu_device {
 
 	struct amdgpu_reset_domain	*reset_domain;
 
+#ifdef CONFIG_DEV_COREDUMP
+	struct amdgpu_coredump_info	*coredump;
+	struct work_struct		coredump_work;
+#endif
+
 	struct mutex			benchmark_mutex;
 
 	bool                            scpm_enabled;

drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c

@@ -32,8 +32,13 @@ void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
 		     bool vram_lost, struct amdgpu_job *job)
 {
 }
+void amdgpu_coredump_init(struct amdgpu_device *adev)
+{
+}
 #else
 
+#define AMDGPU_CORE_DUMP_SIZE_MAX (256 * 1024 * 1024)
+
 const char *hw_ip_names[MAX_HWIP] = {
 	[GC_HWIP]		= "GC",
 	[HDP_HWIP]		= "HDP",
@@ -196,11 +201,9 @@ static void amdgpu_devcoredump_fw_info(struct amdgpu_device *adev,
 }
 
 static ssize_t
-amdgpu_devcoredump_read(char *buffer, loff_t offset, size_t count,
-			void *data, size_t datalen)
+amdgpu_devcoredump_format(char *buffer, size_t count, struct amdgpu_coredump_info *coredump)
 {
 	struct drm_printer p;
-	struct amdgpu_coredump_info *coredump = data;
 	struct drm_print_iterator iter;
 	struct amdgpu_vm_fault_info *fault_info;
 	struct amdgpu_ip_block *ip_block;
@@ -208,7 +211,6 @@ amdgpu_devcoredump_read(char *buffer, loff_t offset, size_t count,
 
 	iter.data = buffer;
 	iter.offset = 0;
-	iter.start = offset;
 	iter.remain = count;
 
 	p = drm_coredump_printer(&iter);
@@ -322,9 +324,63 @@ amdgpu_devcoredump_read(char *buffer, loff_t offset, size_t count,
 	return count - iter.remain;
 }
 
+static ssize_t
+amdgpu_devcoredump_read(char *buffer, loff_t offset, size_t count,
+			void *data, size_t datalen)
+{
+	struct amdgpu_coredump_info *coredump = data;
+	ssize_t byte_copied;
+
+	if (!coredump)
+		return -ENODEV;
+
+	if (!coredump->formatted)
+		return -ENODEV;
+
+	if (offset >= coredump->formatted_size)
+		return 0;
+
+	byte_copied = count < coredump->formatted_size - offset ? count :
+		coredump->formatted_size - offset;
+	memcpy(buffer, coredump->formatted + offset, byte_copied);
+
+	return byte_copied;
+}
+
 static void amdgpu_devcoredump_free(void *data)
 {
-	kfree(data);
+	struct amdgpu_coredump_info *coredump = data;
+
+	kvfree(coredump->formatted);
+	kvfree(data);
+}
+
+static void amdgpu_devcoredump_deferred_work(struct work_struct *work)
+{
+	struct amdgpu_device *adev = container_of(work, typeof(*adev), coredump_work);
+	struct amdgpu_coredump_info *coredump = adev->coredump;
+
+	/* Do a one-time preparation of the coredump output because
+	 * repeatingly calling drm_coredump_printer is very slow.
+	 */
+	coredump->formatted_size = amdgpu_devcoredump_format(
+		NULL, AMDGPU_CORE_DUMP_SIZE_MAX, coredump);
+	coredump->formatted = kvzalloc(coredump->formatted_size, GFP_KERNEL);
+	if (!coredump->formatted) {
+		amdgpu_devcoredump_free(coredump);
+		goto end;
+	}
+
+	amdgpu_devcoredump_format(coredump->formatted, coredump->formatted_size, coredump);
+
+	/* If there's an existing coredump for this device, the free function will be
+	 * called immediately so coredump might be invalid after the call to dev_coredumpm.
+	 */
+	dev_coredumpm(coredump->adev->dev, THIS_MODULE, coredump, 0, GFP_NOWAIT,
+		      amdgpu_devcoredump_read, amdgpu_devcoredump_free);
+
+end:
+	adev->coredump = NULL;
 }
 
 void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
@@ -334,6 +390,10 @@ void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
 	struct amdgpu_coredump_info *coredump;
 	struct drm_sched_job *s_job;
 
+	/* No need to generate a new coredump if there's one in progress already. */
+	if (work_pending(&adev->coredump_work))
+		return;
+
 	coredump = kzalloc_obj(*coredump, GFP_NOWAIT);
 	if (!coredump)
 		return;
@@ -360,11 +420,20 @@ void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
 
 	ktime_get_ts64(&coredump->reset_time);
 
-	dev_coredumpm(dev->dev, THIS_MODULE, coredump, 0, GFP_NOWAIT,
-		      amdgpu_devcoredump_read, amdgpu_devcoredump_free);
+	/* Update the current coredump pointer (no lock needed, this function can only be called
+	 * from a single thread)
+	 */
+	adev->coredump = coredump;
+	/* Kick off coredump formatting to a worker thread. */
+	queue_work(system_unbound_wq, &adev->coredump_work);
 
 	drm_info(dev, "AMDGPU device coredump file has been created\n");
 	drm_info(dev, "Check your /sys/class/drm/card%d/device/devcoredump/data\n",
 		 dev->primary->index);
 }
+
+void amdgpu_coredump_init(struct amdgpu_device *adev)
+{
+	INIT_WORK(&adev->coredump_work, amdgpu_devcoredump_deferred_work);
+}
 #endif

drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h

@@ -35,12 +35,19 @@ struct amdgpu_coredump_info {
 	struct amdgpu_device            *adev;
 	struct amdgpu_task_info         reset_task_info;
 	struct timespec64               reset_time;
+
 	bool                            skip_vram_check;
 	bool                            reset_vram_lost;
 	struct amdgpu_ring              *ring;
+	/* Readable form of coredevdump, generate once to speed up
+	 * reading it (see drm_coredump_printer's documentation).
+	 */
+	ssize_t				formatted_size;
+	char				*formatted;
 };
 #endif
 
 void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
 		     bool vram_lost, struct amdgpu_job *job);
+void amdgpu_coredump_init(struct amdgpu_device *adev);
 #endif

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -3781,6 +3781,8 @@ int amdgpu_device_init(struct amdgpu_device *adev,
 	INIT_WORK(&adev->xgmi_reset_work, amdgpu_device_xgmi_reset_func);
 	INIT_WORK(&adev->userq_reset_work, amdgpu_userq_reset_work);
 
+	amdgpu_coredump_init(adev);
+
 	adev->gfx.gfx_off_req_count = 1;
 	adev->gfx.gfx_off_residency = 0;
 	adev->gfx.gfx_off_entrycount = 0;