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UPSTREAM: 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>
(cherry picked from commit 6a6e5ef2b27f45c15cca569a0825dfd75f564c35)

Bug: 146055070
Bug: 145972256
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Change-Id: I8ea0a4c44fe3496d13a09bcf4922e8aa5cdb78ba
This commit is contained in:
Kalesh Singh
2021-10-29 11:33:29 -07:00
parent bfc28100cf
commit 70fa2e2789
1 changed files with 11 additions and 0 deletions
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11
kernel/trace/trace.c
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@@ -5629,6 +5629,7 @@ 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"
@@ -5640,6 +5641,16 @@ 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"