[PATCH v1 1/7] drm/amdgpu: make devcoredump reading fast

[Pierre-Eric Pelloux-Prayer]

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.

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

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
---
 .../gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c  | 43 +++++++++++++++++--
 .../gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h  |  7 +++
 2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c
index 7b50741dc097..de70747a099d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.c
@@ -34,6 +34,8 @@ void amdgpu_coredump(struct amdgpu_device *adev, bool skip_vram_check,
 }
 #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 +198,9 @@ 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_read(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 +208,6 @@ 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);
@@ -321,8 +320,44 @@ 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->read.buffer) {
+		/* Do a one-time preparation of the coredump output because
+		 * repeatingly calling drm_coredump_printer is very slow.
+		 */
+		coredump->read.size =
+			__amdgpu_devcoredump_read(NULL, AMDGPU_CORE_DUMP_SIZE_MAX, coredump);
+		coredump->read.buffer = kvmalloc(coredump->read.size, GFP_USER);
+		if (!coredump->read.buffer)
+			return -ENODEV;
+
+		__amdgpu_devcoredump_read(coredump->read.buffer, coredump->read.size, coredump);
+	}
+
+	if (offset >= coredump->read.size)
+		return 0;
+
+	byte_copied = count < coredump->read.size - offset ? count :
+		coredump->read.size - offset;
+	memcpy(buffer, coredump->read.buffer + offset, byte_copied);
+
+	return byte_copied;
+}
+
 static void amdgpu_devcoredump_free(void *data)
 {
+	struct amdgpu_coredump_info *coredump = data;
+
+	kvfree(coredump->read.buffer);
 	kfree(data);
 }
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h
index ef9772c6bcc9..33f2f6fdfcf7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dev_coredump.h
@@ -38,6 +38,13 @@ struct amdgpu_coredump_info {
 	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).
+	 */
+	struct {
+		ssize_t size;
+		char *buffer;
+	} read;
 };
 #endif
 
-- 
2.43.0