1 files changed, 26 insertions, 8 deletions
diff --git a/scripts/tracing/ftrace-bisect.sh b/scripts/tracing/ftrace-bisect.sh
index 926701162bc8..bb4f59262bbe 100755
--- a/scripts/tracing/ftrace-bisect.sh
+++ b/scripts/tracing/ftrace-bisect.sh
@@ -12,7 +12,7 @@
 #   (note, if this is a problem with function_graph tracing, then simply
 #    replace "function" with "function_graph" in the following steps).
 #
-#  # cd /sys/kernel/debug/tracing
+#  # cd /sys/kernel/tracing
 #  # echo schedule > set_ftrace_filter
 #  # echo function > current_tracer
 #
@@ -20,22 +20,40 @@
 #
 #  # echo nop > current_tracer
 #
-#  # cat available_filter_functions > ~/full-file
+# Starting with v5.1 this can be done with numbers, making it much faster:
+#
+# The old (slow) way, for kernels before v5.1.
+#
+# [old-way] # cat available_filter_functions > ~/full-file
+#
+# [old-way] *** Note ***  this process will take several minutes to update the
+# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we
+# [old-way] are dealing with thousands of functions. So go have coffee, talk
+# [old-way] with your coworkers, read facebook. And eventually, this operation
+# [old-way] will end.
+#
+# The new way (using numbers) is an O(n) operation, and usually takes less than a second.
+#
+# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file
+#
+# This will create a sequence of numbers that match the functions in
+# available_filter_functions, and when echoing in a number into the
+# set_ftrace_filter file, it will enable the corresponding function in
+# O(1) time. Making enabling all functions O(n) where n is the number of
+# functions to enable.
+#
+# For either the new or old way, the rest of the operations remain the same.
+#
 #  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
 #  # cat ~/test-file > set_ftrace_filter
 #
-# *** Note *** this will take several minutes. Setting multiple functions is
-# an O(n^2) operation, and we are dealing with thousands of functions. So go
-# have  coffee, talk with your coworkers, read facebook. And eventually, this
-# operation will end.
-#
 #  # echo function > current_tracer
 #
 # If it crashes, we know that ~/test-file has a bad function.
 #
 #   Reboot back to test kernel.
 #
-#     # cd /sys/kernel/debug/tracing
+#     # cd /sys/kernel/tracing
 #     # mv ~/test-file ~/full-file
 #
 # If it didn't crash.