Commit 6a6e5ef2 authored by Kalesh Singh's avatar Kalesh Singh Committed by Steven Rostedt (VMware)
Browse files

tracing/histogram: Document hist trigger variables 

Update the tracefs README to describe how hist trigger variables
can be created.

Link: https://lkml.kernel.org/r/20211029183339.3216491-4-kaleshsingh@google.com



Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: default avatarKalesh Singh <kaleshsingh@google.com>
Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 0ca6d12c

kernel/trace/trace.c

+11 −0
Original line number Diff line number Diff line
@@ -5606,6 +5606,7 @@ static const char readme_msg[] = 
#ifdef CONFIG_HIST_TRIGGERS

	"      hist trigger\t- If set, event hits are aggregated into a hash table\n"

	"\t    Format: hist:keys=<field1[,field2,...]>\n"

	"\t            [:<var1>=<field|var_ref|numeric_literal>[,<var2>=...]]\n"

	"\t            [:values=<field1[,field2,...]>]\n"

	"\t            [:sort=<field1[,field2,...]>]\n"

	"\t            [:size=#entries]\n"
@@ -5617,6 +5618,16 @@ static const char readme_msg[] = 
	"\t            common_timestamp - to record current timestamp\n"

	"\t            common_cpu - to record the CPU the event happened on\n"

	"\n"

	"\t    A hist trigger variable can be:\n"

	"\t        - a reference to a field e.g. x=current_timestamp,\n"

	"\t        - a reference to another variable e.g. y=$x,\n"

	"\t        - a numeric literal: e.g. ms_per_sec=1000,\n"

	"\t        - an arithmetic expression: e.g. time_secs=current_timestamp/1000\n"

	"\n"

	"\t    hist trigger aritmethic expressions support addition(+), subtraction(-),\n"

	"\t    multiplication(*) and division(/) operators. An operand can be either a\n"

	"\t    variable reference, field or numeric literal.\n"

	"\n"

	"\t    When a matching event is hit, an entry is added to a hash\n"

	"\t    table using the key(s) and value(s) named, and the value of a\n"

	"\t    sum called 'hitcount' is incremented.  Keys and values\n"