From 6a6e5ef2b27f45c15cca569a0825dfd75f564c35 Mon Sep 17 00:00:00 2001 From: Kalesh Singh Date: Fri, 29 Oct 2021 11:33:29 -0700 Subject: [PATCH] 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 Cc: Ingo Molnar Cc: Shuah Khan Cc: Tom Zanussi Signed-off-by: Kalesh Singh Acked-by: Masami Hiramatsu Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/trace.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 985390cb8441..31a4632f9af1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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=\n" + "\t [:=[,=...]]\n" "\t [:values=]\n" "\t [:sort=]\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"