[PATCH v11 12/19] drm_print: wrap drm_dbg in _dynamic_func_call_no_desc

Jim Cromie
2022-01-07T05:30:21Z

Change __drm_dbg() macro to be CONFIG_DRM_USE_DYNAMIC_DEBUG dependent:
N- keep straight mapping to exported ___drm_dbg()
Y- wrap ___drm_dbg() inside _dynamic_func_call_no_desc()

This patch places ~1/2 of drm.debug API messages behind dyndbg's
JUMP_LABEL/NOOP optimization.

The CONFIG_DRM_USE_DYNAMIC_DEBUG dependence is due to the .data
footprint cost of per-callsite control; 56 bytes/site * ~2k,3k
callsites (for i915, amdgpu), which is significant enough to make
optional.

bash-5.1# drms_load
[ 7.489844] dyndbg: 239 debug prints in module drm
[ 7.494010] ACPI: bus type drm_connector registered
[ 7.546076] dyndbg: 81 debug prints in module drm_kms_helper
[ 7.555723] dyndbg: 2 debug prints in module ttm
[ 7.558920] dyndbg: 8 debug prints in module video
[ 8.074699] dyndbg: 431 debug prints in module i915
[ 8.158682] AMD-Vi: AMD IOMMUv2 functionality not available on this system - This is not a bug.
[ 8.574456] dyndbg: 3817 debug prints in module amdgpu
[ 8.589962] [drm] amdgpu kernel modesetting enabled.
[ 8.590548] amdgpu: CRAT table not found
[ 8.590998] amdgpu: Virtual CRAT table created for CPU
[ 8.591634] amdgpu: Topology: Add CPU node
[ 8.636446] dyndbg: 3 debug prints in module wmi
[ 8.768667] dyndbg: 24 debug prints in module nouveau

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
include/drm/drm_print.h | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 1eef315a0a65..8d6b74270c50 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -319,10 +319,36 @@ enum drm_debug_category {
DRM_UT_DRMRES
};

+/*
+ * 3 name flavors of drm_debug_enabled:
+ * drm_debug_enabled - public/legacy, always checks bits
+ * _drm_debug_enabled - instrumented to observe call-rates, est overheads.
+ * __drm_debug_enabled - privileged - knows jump-label state, can short-circuit
+ */
static inline bool drm_debug_enabled(enum drm_debug_category category)
{
return unlikely(__drm_debug & BIT(category));
}
+/*
+ * Wrap fn in macro, so that the pr_debug sees the actual caller, not
+ * the inline fn. Using this name creates a callsite entry / control
+ * point in /proc/dynamic_debug/control.
+ */
+#define _drm_debug_enabled(category) \
+ ({ \
+ pr_debug("todo: maybe avoid via dyndbg\n"); \
+ drm_debug_enabled(category); \
+ })
+#if defined(CONFIG_DRM_USE_DYNAMIC_DEBUG)
+/*
+ * dyndbg is wrapping the drm.debug API, so as to avoid the runtime
+ * bit-test overheads of drm_debug_enabled() in those api calls.
+ * In this case, executed callsites are known enabled, so true.
+ */
+#define __drm_debug_enabled(category) true
+#else
+#define __drm_debug_enabled(category) drm_debug_enabled(category)
+#endif

/*
* struct device based logging
@@ -497,7 +523,13 @@ void ___drm_dbg(enum drm_debug_category category, const char *format, ...);
__printf(1, 2)
void __drm_err(const char *format, ...);

+#if !defined(CONFIG_DRM_USE_DYNAMIC_DEBUG)
#define __drm_dbg(fmt, ...) ___drm_dbg(fmt, ##__VA_ARGS__)
+#else
+#define __drm_dbg(eCat, fmt, ...) \
+ _dynamic_func_call_no_desc(fmt, ___drm_dbg, \
+ eCat, fmt, ##__VA_ARGS__)
+#endif

/* Macros to make printk easier */

@@ -569,7 +601,7 @@ void __drm_err(const char *format, ...);
static DEFINE_RATELIMIT_STATE(rs_, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);\
const struct drm_device *drm_ = (drm); \
\
- if (drm_debug_enabled(DRM_UT_ ## category) && __ratelimit(&rs_)) \
+ if (__drm_debug_enabled(DRM_UT_ ## category) && __ratelimit(&rs_)) \
drm_dev_printk(drm_ ? drm_->dev : NULL, KERN_DEBUG, fmt, ## __VA_ARGS__); \
})

--
2.33.1