[PATCH v4] drm/trace: Buffer DRM logs in a ringbuffer accessible via debugfs
Sean Paul
sean at poorly.run
Tue Jan 14 17:21:43 UTC 2020
From: Sean Paul <seanpaul at chromium.org>
This patch uses a ring_buffer to keep a "flight recorder" (name credit Weston)
of DRM logs for a specified set of debug categories. The user writes a
bitmask of debug categories to the "trace_mask" node and can read log
messages from the "trace" node.
These nodes currently exist in debugfs under the dri directory. I
intended on exposing all of this through tracefs originally, but the
tracefs entry points are not exposed, so there's no way to create
tracefs files from drivers at the moment. I think it would be a
worthwhile endeavour, but one requiring more time and conversation to
ensure the drm traces fit somewhere sensible.
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: David Airlie <airlied at gmail.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Pekka Paalanen <ppaalanen at gmail.com>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Sean Paul <seanpaul at chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3
Changes in v2:
- Went with a completely different approach:
https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html
Changes in v3:
- Changed commit message to be a bit less RFC-y
- Make class_drm_category_log an actual trace class
Changes in v4:
- Instead of [ab]using trace events and the system trace buffer, use our
own ringbuffer
---
---
Documentation/gpu/drm-uapi.rst | 9 +
drivers/gpu/drm/Kconfig | 1 +
drivers/gpu/drm/Makefile | 2 +-
drivers/gpu/drm/drm_drv.c | 3 +
drivers/gpu/drm/drm_print.c | 80 +++++--
drivers/gpu/drm/drm_trace.c | 376 +++++++++++++++++++++++++++++++++
include/drm/drm_print.h | 39 ++++
7 files changed, 487 insertions(+), 23 deletions(-)
create mode 100644 drivers/gpu/drm/drm_trace.c
diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 56fec6ed1ad8..089eb6fd3e94 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -312,6 +312,15 @@ Debugfs Support
.. kernel-doc:: drivers/gpu/drm/drm_debugfs.c
:export:
+DRM Tracing
+---------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_trace.c
+ :doc: DRM Tracing
+
+.. kernel-doc:: drivers/gpu/drm/drm_trace.c
+ :internal:
+
Sysfs Support
=============
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index d0aa6cff2e02..9d8077e87afe 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -14,6 +14,7 @@ menuconfig DRM
select I2C
select I2C_ALGOBIT
select DMA_SHARED_BUFFER
+ select RING_BUFFER
select SYNC_FILE
help
Kernel-level support for the Direct Rendering Infrastructure (DRI)
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 6493088a0fdd..88b4674934e6 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -29,7 +29,7 @@ drm-$(CONFIG_DRM_PANEL) += drm_panel.o
drm-$(CONFIG_OF) += drm_of.o
drm-$(CONFIG_AGP) += drm_agpsupport.o
drm-$(CONFIG_PCI) += drm_pci.o
-drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o
+drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o drm_trace.o
drm-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
drm_vram_helper-y := drm_gem_vram_helper.o \
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 7c18a980cd4b..98260b9f8004 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -1114,6 +1114,7 @@ static const struct file_operations drm_stub_fops = {
static void drm_core_exit(void)
{
unregister_chrdev(DRM_MAJOR, "drm");
+ drm_trace_cleanup();
debugfs_remove(drm_debugfs_root);
drm_sysfs_destroy();
idr_destroy(&drm_minors_idr);
@@ -1135,6 +1136,8 @@ static int __init drm_core_init(void)
drm_debugfs_root = debugfs_create_dir("dri", NULL);
+ WARN_ON(drm_trace_init(drm_debugfs_root));
+
ret = register_chrdev(DRM_MAJOR, "drm", &drm_stub_fops);
if (ret < 0)
goto error;
diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
index 111b932cf2a9..0ac1867937bf 100644
--- a/drivers/gpu/drm/drm_print.c
+++ b/drivers/gpu/drm/drm_print.c
@@ -262,21 +262,37 @@ void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
struct va_format vaf;
va_list args;
- if (!drm_debug_enabled(category))
- return;
-
- va_start(args, format);
- vaf.fmt = format;
- vaf.va = &args;
-
- if (dev)
- dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
- __builtin_return_address(0), &vaf);
- else
- printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
- __builtin_return_address(0), &vaf);
+ if (drm_debug_enabled(category)) {
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
+
+ if (dev)
+ dev_printk(KERN_DEBUG, dev, "[" DRM_NAME ":%ps] %pV",
+ __builtin_return_address(0), &vaf);
+ else
+ printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+ __builtin_return_address(0), &vaf);
+
+ va_end(args);
+ }
- va_end(args);
+ if (drm_trace_enabled(category)) {
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
+
+ if (dev)
+ drm_dev_trace_printf(dev, "[%ps] %pV",
+ __builtin_return_address(0),
+ &vaf);
+ else
+ drm_trace_printf("[%ps] %pV",
+ __builtin_return_address(0),
+ &vaf);
+
+ va_end(args);
+ }
}
EXPORT_SYMBOL(drm_dev_dbg);
@@ -285,17 +301,28 @@ void __drm_dbg(enum drm_debug_category category, const char *format, ...)
struct va_format vaf;
va_list args;
- if (!drm_debug_enabled(category))
- return;
- va_start(args, format);
- vaf.fmt = format;
- vaf.va = &args;
+ if (drm_debug_enabled(category)) {
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
- printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
- __builtin_return_address(0), &vaf);
+ printk(KERN_DEBUG "[" DRM_NAME ":%ps] %pV",
+ __builtin_return_address(0), &vaf);
- va_end(args);
+ va_end(args);
+ }
+
+ if (drm_trace_enabled(category)) {
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
+
+ drm_trace_printf("[%ps] %pV", __builtin_return_address(0),
+ &vaf);
+
+ va_end(args);
+ }
}
EXPORT_SYMBOL(__drm_dbg);
@@ -312,6 +339,15 @@ void __drm_err(const char *format, ...)
__builtin_return_address(0), &vaf);
va_end(args);
+
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
+
+ drm_trace_printf("[%ps] *ERROR* %pV", __builtin_return_address(0),
+ &vaf);
+
+ va_end(args);
}
EXPORT_SYMBOL(__drm_err);
diff --git a/drivers/gpu/drm/drm_trace.c b/drivers/gpu/drm/drm_trace.c
new file mode 100644
index 000000000000..0e7cf342d1d9
--- /dev/null
+++ b/drivers/gpu/drm/drm_trace.c
@@ -0,0 +1,376 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright (C) 2020 Google, Inc.
+ *
+ * Authors:
+ * Sean Paul <seanpaul at chromium.org>
+ */
+
+#include <linux/cpumask.h>
+#include <linux/debugfs.h>
+#include <linux/kernel.h>
+#include <linux/ring_buffer.h>
+#include <linux/slab.h>
+#include <linux/stat.h>
+
+#include <drm/drm_device.h>
+#include <drm/drm_print.h>
+
+#define DRM_TRACE_MAX_LEN 256
+
+/**
+ * DOC: DRM Tracing
+ *
+ * *tl;dr* DRM tracing is a lightweight alternative to traditional DRM debug
+ * logging.
+ *
+ * While DRM logging is quite convenient when reproducing a specific issue, it
+ * doesn't help when something goes wrong unexpectedly. There are a couple
+ * reasons why one does not want to enable DRM logging at all times:
+ *
+ * 1. We don't want to overwhelm syslog with drm spam, others have to use it too
+ * 2. Console logging is slow
+ *
+ * DRM tracing aims to solve both these problems.
+ *
+ * To use DRM tracing, write a DRM debug category mask (this is a bitmask of
+ * &drm_debug_category values) to the trace_mask file:
+ * ::
+ *
+ * eg: echo 0x106 > /sys/kernel/debug/dri/trace_mask
+ *
+ * Once active, all log messages in the specified categories will be written to
+ * the DRM trace. Once at capacity, the trace will overwrite old messages with
+ * new ones. At any point, one can read the trace file to extract the previous N
+ * DRM messages:
+ * ::
+ *
+ * eg: cat /sys/kernel/debug/dri/trace
+ *
+ * Considerations
+ * **************
+ * The contents of the DRM Trace are **not** considered UABI. **DO NOT depend on
+ * the values of these traces in your userspace.** These traces are intended for
+ * entertainment purposes only. The contents of these logs carry no warranty,
+ * expressed or implied.
+ *
+ * New traces can not be added to the trace buffer while it is being read. If
+ * this proves to be a problem, it can be mitigated by making a copy of the
+ * buffer on start of read. Since DRM trace is not meant to be continuously
+ * read, this loss is acceptable.
+ *
+ * The timestamps on logs are CPU-local. As such, log messages from different
+ * CPUs may have slightly different ideas about time.
+ *
+ * Since each CPU has its own buffer, they won't all overflow at the same rate.
+ * This means that messages from a particularly active CPU could be dropped
+ * while an inactive CPU might have much older log messages. So don't be fooled
+ * if you seem to be missing log messages when you see a switch between CPUs in
+ * the logs.
+ *
+ * Internals
+ * *********
+ * The DRM Tracing functions are intentionally unexported, they are not meant to
+ * be used by drivers directly. The reasons are twofold:
+ *
+ * 1. All messages going to traces should also go to the console logs. This
+ * ensures users can choose their logging medium without fear they're losing
+ * messages.
+ * 2. Writing directly to the trace skips category filtering, resulting in trace
+ * spam.
+ */
+
+struct drm_trace_info {
+ struct ring_buffer *buffer;
+ struct dentry *debugfs;
+ struct dentry *debugfs_mask;
+ enum drm_debug_category category_mask;
+};
+static struct drm_trace_info drm_trace;
+
+struct drm_trace_seq_iter {
+ loff_t pos;
+ cpumask_var_t cpu_mask;
+ int cpu;
+ u64 ts;
+};
+
+static void *drm_trace_seq_start(struct seq_file *seq_file, loff_t *pos)
+{
+ struct drm_trace_info *info = seq_file->private;
+ struct drm_trace_seq_iter *iter;
+ int cpu;
+
+ iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+ if (!iter)
+ return NULL;
+
+ if (!zalloc_cpumask_var(&iter->cpu_mask, GFP_KERNEL))
+ return NULL;
+
+ /*
+ * TODO: We could do better than stopping record for the entirety of the
+ * read session.
+ */
+ ring_buffer_record_off(info->buffer);
+
+ /*
+ * pos is only used as a means of determining whether we're at the start
+ * of the virtual file, or continuing a read. We don't want to skip over
+ * log lines since that's not a meaningful thing to do.
+ */
+ iter->pos = *pos;
+
+ iter->cpu = -1;
+
+ /*
+ * There's no way to extract the ring buffer's cpumask, so we'll try
+ * every possible cpu and skip the invalid entries.
+ */
+ for_each_possible_cpu(cpu) {
+ if (ring_buffer_entries_cpu(info->buffer, cpu))
+ cpumask_set_cpu(cpu, iter->cpu_mask);
+ }
+
+ return iter;
+}
+
+static void *drm_trace_seq_next(struct seq_file *seq_file, void *data,
+ loff_t *pos)
+{
+ struct drm_trace_info *info = seq_file->private;
+ struct drm_trace_seq_iter *iter = data;
+ int cpu;
+
+ *pos = ++iter->pos;
+ iter->cpu = -1;
+ iter->ts = 0;
+
+ /* Find the oldest event across our cpu_mask */
+ for_each_cpu(cpu, iter->cpu_mask) {
+ u64 ts;
+
+ if (!ring_buffer_peek(info->buffer, cpu, &ts, NULL)) {
+ cpumask_clear_cpu(cpu, iter->cpu_mask);
+ continue;
+ }
+ if (iter->cpu == -1 || ts < iter->ts) {
+ iter->ts = ts;
+ iter->cpu = cpu;
+ }
+ }
+ if (iter->cpu == -1)
+ return NULL;
+
+ return iter;
+}
+
+static void drm_trace_seq_stop(struct seq_file *seq_file, void *data)
+{
+ struct drm_trace_info *info = seq_file->private;
+ struct drm_trace_seq_iter *iter = data;
+
+ free_cpumask_var(iter->cpu_mask);
+ kfree(iter);
+
+ ring_buffer_record_on(info->buffer);
+}
+
+static int drm_trace_seq_show(struct seq_file *seq_file, void *data)
+{
+ struct drm_trace_info *info = seq_file->private;
+ struct drm_trace_seq_iter *iter = data;
+ struct ring_buffer_event *event;
+ u64 ts, usec;
+
+ if (iter->pos == 0) {
+ seq_printf(seq_file, "[%3s %12s] %s\n", "cpu", "timestamp",
+ "message");
+ return 0;
+ } else if (iter->cpu == -1) {
+ /* This happens when we start a session with position > 0 */
+ return SEQ_SKIP;
+ }
+
+ event = ring_buffer_consume(info->buffer, iter->cpu, &ts, NULL);
+
+ ts += 500;
+ /* ts converts from ns->us */
+ do_div(ts, 1000);
+ /* ts converts from us->s */
+ usec = do_div(ts, USEC_PER_SEC);
+
+ seq_printf(seq_file, "[%3u %5llu.%06llu] %s", iter->cpu, ts, usec,
+ (const char *)ring_buffer_event_data(event));
+
+ return 0;
+}
+
+static const struct seq_operations drm_trace_sops = {
+ .start = drm_trace_seq_start,
+ .next = drm_trace_seq_next,
+ .stop = drm_trace_seq_stop,
+ .show = drm_trace_seq_show
+};
+
+static int drm_trace_fop_open(struct inode *inode, struct file *file)
+{
+ struct seq_file *seq_file;
+ int ret;
+
+ ret = seq_open(file, &drm_trace_sops);
+ if (ret)
+ return ret;
+
+ seq_file = (struct seq_file *)file->private_data;
+ seq_file->private = inode->i_private; /* this is drm_trace_info */
+
+ return 0;
+}
+
+static const struct file_operations drm_trace_fops = {
+ .open = drm_trace_fop_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
+/**
+ * drm_trace_init - initializes tracing for drm core
+ * @debugfs_root: the dentry for drm core's debugfs root
+ *
+ * This function is called on drm core init. It is responsible for initializing
+ * drm tracing. This function must be matched by a call to drm_trace_cleanup().
+ *
+ * Returns: 0 on success, -errno on failure
+ */
+int drm_trace_init(struct dentry *debugfs_root)
+{
+ struct drm_trace_info *info = &drm_trace;
+ int ret;
+
+ info->buffer = ring_buffer_alloc(PAGE_SIZE * 2, RB_FL_OVERWRITE);
+ if (!info->buffer)
+ return -ENOMEM;
+
+ info->debugfs_mask = debugfs_create_u32("trace_mask",
+ S_IFREG | S_IRUGO | S_IWUSR,
+ debugfs_root,
+ &info->category_mask);
+ if (IS_ERR(info->debugfs)) {
+ ret = PTR_ERR(info->debugfs);
+ goto err_debugfs_mask;
+ }
+
+ info->debugfs = debugfs_create_file("trace", S_IFREG | S_IRUGO,
+ debugfs_root, info,
+ &drm_trace_fops);
+ if (IS_ERR(info->debugfs)) {
+ ret = PTR_ERR(info->debugfs);
+ goto err_debugfs;
+ }
+
+ return 0;
+
+err_debugfs_mask:
+ debugfs_remove(info->debugfs_mask);
+err_debugfs:
+ ring_buffer_free(info->buffer);
+ return ret;
+}
+
+/**
+ * drm_trace_cleanup - cleans up tracing for drm core
+ *
+ * This function is responsible for cleaning up anything that was previously
+ * initialized in drm_trace_init()
+ */
+void drm_trace_cleanup()
+{
+ struct drm_trace_info *info = &drm_trace;
+
+ debugfs_remove(info->debugfs);
+ debugfs_remove(info->debugfs_mask);
+ ring_buffer_free(info->buffer);
+ memset(info, 0, sizeof(*info));
+}
+
+/**
+ * drm_trace_enabled - check if a debug category has traces enabled
+ * @category: the debug category to check
+ *
+ * Returns true if the given category has drm traces enabled, false otherwise.
+ */
+bool drm_trace_enabled(enum drm_debug_category category)
+{
+ return READ_ONCE(drm_trace.category_mask) & category;
+}
+
+static int drm_trace_write(const void *data, unsigned int len)
+{
+ struct drm_trace_info *info = &drm_trace;
+ struct ring_buffer_event *event;
+ void *event_body;
+
+ event = ring_buffer_lock_reserve(info->buffer, len);
+ if (!event)
+ return -ENOMEM;
+
+ event_body = ring_buffer_event_data(event);
+ memcpy(event_body, data, len);
+
+ return ring_buffer_unlock_commit(info->buffer, event);
+}
+
+/**
+ * drm_trace_printf - adds an entry to the drm trace
+ * @format: printf format of the message to add to the trace
+ *
+ * This function adds a new entry in the drm trace.
+ */
+void drm_trace_printf(const char *format, ...)
+{
+ char buf[DRM_TRACE_MAX_LEN];
+ va_list args;
+ int ret;
+
+ va_start(args, format);
+ ret = vsnprintf(buf, sizeof(buf), format, args);
+ va_end(args);
+
+ if (ret < 0)
+ return;
+ else if (ret >= sizeof(buf))
+ ret = sizeof(buf) - 1;
+
+ drm_trace_write(buf, ret + 1);
+}
+
+/**
+ * drm_dev_trace_printf - adds an entry to the drm trace
+ * @dev: pointer to device so we can print the name
+ * @format: printf format of the message to add to the trace
+ *
+ * This function adds a new entry in the drm trace.
+ */
+void drm_dev_trace_printf(const struct device *dev, const char *format, ...)
+{
+ char buf[DRM_TRACE_MAX_LEN];
+ struct va_format vaf;
+ va_list args;
+ int ret;
+
+ va_start(args, format);
+ vaf.fmt = format;
+ vaf.va = &args;
+ ret = snprintf(buf, sizeof(buf), "%s %s: %pV", dev_driver_string(dev),
+ dev_name(dev), &vaf);
+ va_end(args);
+
+ if (ret < 0)
+ return;
+ else if (ret >= sizeof(buf))
+ ret = sizeof(buf) - 1;
+
+ drm_trace_write(buf, ret + 1);
+}
diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 8f99d389792d..1f3dae7150f0 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -320,6 +320,45 @@ static inline bool drm_debug_enabled(enum drm_debug_category category)
return unlikely(__drm_debug & category);
}
+#ifdef CONFIG_DEBUG_FS
+
+int drm_trace_init(struct dentry *debugfs_root);
+bool drm_trace_enabled(enum drm_debug_category category);
+__printf(1, 2)
+void drm_trace_printf(const char *format, ...);
+__printf(2, 3)
+void drm_dev_trace_printf(const struct device *dev, const char *format, ...);
+void drm_trace_cleanup(void);
+
+#else
+
+static inline int drm_trace_init(struct dentry *debugfs_root)
+{
+ return 0;
+}
+
+static inline bool drm_trace_enabled(enum drm_debug_category category)
+{
+ return false;
+}
+
+__printf(1, 2)
+static inline void drm_trace_printf(const char *format, ...)
+{
+}
+
+__printf(2, 3)
+static inline void drm_dev_trace_printf(const struct device *dev,
+ const char *format, ...)
+{
+}
+
+static inline void drm_trace_cleanup(void)
+{
+}
+
+#endif
+
/*
* struct device based logging
*
--
Sean Paul, Software Engineer, Google / Chromium OS
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