Merge remote branch 'keithp/drm-intel-next' of /ssd/git/drm-next into drm-core-next

* 'keithp/drm-intel-next' of /ssd/git/drm-next: (301 commits)
  drm/i915: split PCH clock gating init
  drm/i915: add Ivybridge clock gating init function
  drm/i915: Update the location of the ringbuffers' HWS_PGA registers for IVB.
  drm/i915: Add support for fence registers on Ivybridge.
  drm/i915: Use existing function instead of open-coding fence reg clear.
  drm/i915: split clock gating init into per-chipset functions
  drm/i915: set IBX pch type explicitly
  drm/i915: add Ivy Bridge PCI IDs and driver feature structs
  drm/i915: add PantherPoint PCH ID
  agp/intel: add Ivy Bridge support
  drm/i915: ring support for Ivy Bridge
  drm/i915: page flip support for Ivy Bridge
  drm/i915: interrupt & vblank support for Ivy Bridge
  drm/i915: treat Ivy Bridge watermarks like Sandy Bridge
  drm/i915: manual FDI training for Ivy Bridge
  drm/i915: add swizzle/tiling support for Ivy Bridge
  drm/i915: Ivy Bridge has split display and pipe control
  drm/i915: add IS_IVYBRIDGE macro for checks
  drm/i915: add IS_GEN7 macro to cover Ivy Bridge and later
  drm/i915: split enable/disable vblank code into chipset specific functions
  ...

1 files changed, 40 insertions, 0 deletions

diff --git a/Documentation/workqueue.txt b/Documentation/workqueue.txt
index 01c513fac40..a0b577de918 100644
--- a/Documentation/workqueue.txt
+++ b/Documentation/workqueue.txt
@@ -12,6 +12,7 @@ CONTENTS
 4. Application Programming Interface (API)
 5. Example Execution Scenarios
 6. Guidelines
+7. Debugging
 
 
 1. Introduction
@@ -379,3 +380,42 @@ If q1 has WQ_CPU_INTENSIVE set,
 * Unless work items are expected to consume a huge amount of CPU
   cycles, using a bound wq is usually beneficial due to the increased
   level of locality in wq operations and work item execution.
+
+
+7. Debugging
+
+Because the work functions are executed by generic worker threads
+there are a few tricks needed to shed some light on misbehaving
+workqueue users.
+
+Worker threads show up in the process list as:
+
+root      5671  0.0  0.0      0     0 ?        S    12:07   0:00 [kworker/0:1]
+root      5672  0.0  0.0      0     0 ?        S    12:07   0:00 [kworker/1:2]
+root      5673  0.0  0.0      0     0 ?        S    12:12   0:00 [kworker/0:0]
+root      5674  0.0  0.0      0     0 ?        S    12:13   0:00 [kworker/1:0]
+
+If kworkers are going crazy (using too much cpu), there are two types
+of possible problems:
+
+	1. Something beeing scheduled in rapid succession
+	2. A single work item that consumes lots of cpu cycles
+
+The first one can be tracked using tracing:
+
+	$ echo workqueue:workqueue_queue_work > /sys/kernel/debug/tracing/set_event
+	$ cat /sys/kernel/debug/tracing/trace_pipe > out.txt
+	(wait a few secs)
+	^C
+
+If something is busy looping on work queueing, it would be dominating
+the output and the offender can be determined with the work item
+function.
+
+For the second type of problems it should be possible to just check
+the stack trace of the offending worker thread.
+
+	$ cat /proc/THE_OFFENDING_KWORKER/stack
+
+The work item's function should be trivially visible in the stack
+trace.