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2024-05-10 10ebd8556b7990499c896a550e3d416b444211e6

 kernel/scripts/tracing/ftrace-bisect.sh
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@@ -12,7 +12,7 @@
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 #   (note, if this is a problem with function_graph tracing, then simply
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 #    replace "function" with "function_graph" in the following steps).
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 #
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-#  # cd /sys/kernel/debug/tracing
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+#  # cd /sys/kernel/tracing
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 #  # echo schedule > set_ftrace_filter
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 #  # echo function > current_tracer
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 #
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@@ -20,14 +20,32 @@
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 #
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 #  # echo nop > current_tracer
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 #
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-#  # cat available_filter_functions > ~/full-file
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+# Starting with v5.1 this can be done with numbers, making it much faster:
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+#
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+# The old (slow) way, for kernels before v5.1.
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+#
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+# [old-way] # cat available_filter_functions > ~/full-file
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+#
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+# [old-way] *** Note ***  this process will take several minutes to update the
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+# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we
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+# [old-way] are dealing with thousands of functions. So go have coffee, talk
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+# [old-way] with your coworkers, read facebook. And eventually, this operation
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+# [old-way] will end.
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+#
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+# The new way (using numbers) is an O(n) operation, and usually takes less than a second.
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+#
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+# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file
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+#
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+# This will create a sequence of numbers that match the functions in
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+# available_filter_functions, and when echoing in a number into the
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+# set_ftrace_filter file, it will enable the corresponding function in
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+# O(1) time. Making enabling all functions O(n) where n is the number of
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+# functions to enable.
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+#
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+# For either the new or old way, the rest of the operations remain the same.
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+#
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 #  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
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 #  # cat ~/test-file > set_ftrace_filter
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-#
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-# *** Note *** this will take several minutes. Setting multiple functions is
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-# an O(n^2) operation, and we are dealing with thousands of functions. So go
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-# have  coffee, talk with your coworkers, read facebook. And eventually, this
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-# operation will end.
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 #
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 #  # echo function > current_tracer
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 #
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@@ -35,7 +53,7 @@
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 #
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 #   Reboot back to test kernel.
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 #
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-#     # cd /sys/kernel/debug/tracing
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+#     # cd /sys/kernel/tracing
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 #     # mv ~/test-file ~/full-file
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 #
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 # If it didn't crash.