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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 #ifdef CONFIG_HIST_TRIGGERS
" hist trigger\t- If set, event hits are aggregated into a hash table\n" " hist trigger\t- If set, event hits are aggregated into a hash table\n"
"\t Format: hist:keys=<field1[,field2,...]>\n" "\t Format: hist:keys=<field1[,field2,...]>\n"
"\t [:<var1>=<field|var_ref|numeric_literal>[,<var2>=...]]\n"
"\t [:values=<field1[,field2,...]>]\n" "\t [:values=<field1[,field2,...]>]\n"
"\t [:sort=<field1[,field2,...]>]\n" "\t [:sort=<field1[,field2,...]>]\n"
"\t [:size=#entries]\n" "\t [:size=#entries]\n"
@ -5617,6 +5618,16 @@ static const char readme_msg[] =
"\t common_timestamp - to record current timestamp\n" "\t common_timestamp - to record current timestamp\n"
"\t common_cpu - to record the CPU the event happened on\n" "\t common_cpu - to record the CPU the event happened on\n"
"\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 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 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" "\t sum called 'hitcount' is incremented. Keys and values\n"