linux-kernel - [PATCH v8 14/16] drm_print: instrument drm_debug

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Date:   Wed, 15 Sep 2021 10:39:55 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, daniel@...ll.ch
Cc:     Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH v8 14/16] drm_print: instrument drm_debug_enabled

Duplicate drm_debug_enabled() code into both "basic" and "dyndbg"
ifdef branches.  Then add a pr_debug("todo: ...") into the "dyndbg"
branch.

Then convert the "dyndbg" branch's code to a macro, so that the
pr_debug() get its callsite info from the invoking function, instead
of from drm_debug_enabled() itself.

This gives us unique callsite info for the 8 remaining users of
drm_debug_enabled(), and lets us enable them individually to see how
much logging traffic they generate.  The oft-visited callsites can
then be reviewed for runtime cost and possible optimizations.

Heres what we get:

bash-5.1# modprobe drm
dyndbg: 384 debug prints in module drm
bash-5.1# grep todo: /proc/dynamic_debug/control
drivers/gpu/drm/drm_edid.c:1843 [drm]connector_bad_edid =_ "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_print.c:309 [drm]___drm_dbg =p "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_print.c:286 [drm]__drm_dev_dbg =p "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_vblank.c:1491 [drm]drm_vblank_restore =_ "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_vblank.c:787 [drm]drm_crtc_vblank_helper_get_vblank_timestamp_internal =_ "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_vblank.c:410 [drm]drm_crtc_accurate_vblank_count =_ "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_atomic_uapi.c:1457 [drm]drm_mode_atomic_ioctl =_ "todo: maybe avoid via dyndbg\012"
drivers/gpu/drm/drm_edid_load.c:178 [drm]edid_load =_ "todo: maybe avoid via dyndbg\012"

At quick glance, edid won't qualify, drm_print might, drm_vblank is
strongest chance, maybe atomic-ioctl too.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
---
 include/drm/drm_print.h | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/drm/drm_print.h b/include/drm/drm_print.h
index 4a38591a424b..c9cabc8db672 100644
--- a/include/drm/drm_print.h
+++ b/include/drm/drm_print.h
@@ -381,6 +381,11 @@ enum drm_debug_category {
 #define DRM_DBG_CAT_DP		DRM_UT_DP
 #define DRM_DBG_CAT_DRMRES	DRM_UT_DRMRES
 
+static inline bool drm_debug_enabled(enum drm_debug_category category)
+{
+	return unlikely(__drm_debug & category);
+}
+
 #else /* CONFIG_DRM_USE_DYNAMIC_DEBUG */
 
 /* join prefix + format in cpp so dyndbg can see it */
@@ -414,12 +419,13 @@ enum drm_debug_category {
 #define DRM_DBG_CAT_DP		"drm:dp:"
 #define DRM_DBG_CAT_DRMRES	"drm:res:"
 
-#endif /* CONFIG_DRM_USE_DYNAMIC_DEBUG */
+#define drm_debug_enabled(category)			\
+	({						\
+	pr_debug("todo: maybe avoid via dyndbg\n");	\
+	unlikely(__drm_debug & (category));		\
+	})
 
-static inline bool drm_debug_enabled(enum drm_debug_category category)
-{
-	return unlikely(__drm_debug & category);
-}
+#endif /* CONFIG_DRM_USE_DYNAMIC_DEBUG */
 
 /*
  * struct device based logging
@@ -569,7 +575,6 @@ void __drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
 #define drm_dbg_drmres(drm, fmt, ...)					\
 	drm_dev_dbg((drm) ? (drm)->dev : NULL, DRM_DBG_CAT_DRMRES, fmt, ##__VA_ARGS__)
 
-
 /*
  * printk based logging
  *
-- 
2.31.1