From: Steven Rostedt <rostedt@goodmis.org>
To: Kalesh Singh <kaleshsingh@google.com>
Cc: surenb@google.com, hridya@google.com, namhyung@kernel.org,
kernel-team@android.com, Jonathan Corbet <corbet@lwn.net>,
Ingo Molnar <mingo@redhat.com>, Shuah Khan <shuah@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Tom Zanussi <zanussi@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v2 3/5] tracing: Fix operator precedence for hist triggers expression
Date: Wed, 20 Oct 2021 11:48:05 -0400 [thread overview]
Message-ID: <20211020114805.3fbb7d94@gandalf.local.home> (raw)
In-Reply-To: <20211020013153.4106001-4-kaleshsingh@google.com>
On Tue, 19 Oct 2021 18:31:40 -0700
Kalesh Singh <kaleshsingh@google.com> wrote:
> @@ -2391,60 +2460,61 @@ static int check_expr_operands(struct trace_array *tr,
> static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> struct trace_event_file *file,
> char *str, unsigned long flags,
> - char *var_name, unsigned int level)
> + char *var_name, unsigned int *n_subexprs)
> {
> struct hist_field *operand1 = NULL, *operand2 = NULL, *expr = NULL;
> unsigned long operand_flags;
> int field_op, ret = -EINVAL;
> char *sep, *operand1_str;
>
> - if (level > 3) {
> + if (*n_subexprs > 3) {
Why limit the sub expressions, and not just keep the limit of the level of
recursion. We allow 3 levels of recursion, but we could have more than 3
sub expressions.
If we have: a * b + c / d - e * f / h
It would break down into:
-
+ /
* / * h
a b c d e f
Which I believe is 6 "sub expressions", but never goes more than three deep
in recursion:
"a * b + c / d - e * f / h"
Step 1:
op = "-"
operand1 = "a * b + c / d"
operand2 = "e * f / h"
Process operand1: (recursion level 1)
op = "+"
operand1a = "a * b"
operand2a = "c / d"
Process operand1a: (recursion level 2)
op = "*"
operand1b = "a"
operand2b = "b"
return;
Process operand1b: (recursion level 2)
op = "/"
operand1b = "c"
operand2b = "d"
return;
return;
Process operand2: (recursion level 1)
op = "/"
operand1c = "e * f"
operand2c = "h"
Process operand1c: (recursion level 2)
op = "*"
operand1c = "e"
operand2c = "f"
return;
return;
> +
> + /* LHS of string is an expression e.g. a+b in a+b+c */
> + operand1 = parse_expr(hist_data, file, operand1_str, operand_flags, NULL, n_subexprs);
> if (IS_ERR(operand1)) {
> ret = PTR_ERR(operand1);
> operand1 = NULL;
I wonder if we should look for optimizations, in case of operand1 and
operand2 are both constants?
Just perform the function, and convert it into a constant as well.
-- Steve
next prev parent reply other threads:[~2021-10-20 15:48 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-20 1:31 [PATCH v2 0/5] tracing: Extend histogram triggers expression parsing Kalesh Singh
2021-10-20 1:31 ` [PATCH v2 1/5] tracing: Add support for creating hist trigger variables from literal Kalesh Singh
2021-10-20 15:32 ` Steven Rostedt
2021-10-20 15:55 ` Kalesh Singh
2021-10-20 15:59 ` Steven Rostedt
2021-10-20 1:31 ` [PATCH v2 2/5] tracing: Add division and multiplication support for hist triggers Kalesh Singh
2021-10-20 2:27 ` Steven Rostedt
2021-10-20 14:54 ` Kalesh Singh
2021-10-20 15:13 ` Steven Rostedt
2021-10-20 15:23 ` Kalesh Singh
2021-10-20 1:31 ` [PATCH v2 3/5] tracing: Fix operator precedence for hist triggers expression Kalesh Singh
2021-10-20 14:28 ` Steven Rostedt
2021-10-20 15:06 ` Kalesh Singh
2021-10-20 15:13 ` Steven Rostedt
2021-10-20 15:48 ` Steven Rostedt [this message]
2021-10-20 16:11 ` Kalesh Singh
2021-10-20 16:19 ` Steven Rostedt
2021-10-20 16:22 ` Kalesh Singh
2021-10-20 1:31 ` [PATCH v2 4/5] tracing/selftests: Add tests for hist trigger expression parsing Kalesh Singh
2021-10-20 1:31 ` [PATCH v2 5/5] tracing/histogram: Document expression arithmetic and constants Kalesh Singh
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