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tracing/histogram: Document hist trigger variables

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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: Kalesh Singh <kaleshsingh@google.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Kalesh Singh 2021-10-29 11:33:29 -07:00 committed by Steven Rostedt (VMware)
parent 0ca6d12c97
commit 6a6e5ef2b2
1 changed files with 11 additions and 0 deletions
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11
kernel/trace/trace.c
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@ -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"