From: Kalesh Singh <kaleshsingh@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>,
Hridya Valsaraju <hridya@google.com>,
Namhyung Kim <namhyung@kernel.org>,
"Cc: Android Kernel" <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>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH v2 3/5] tracing: Fix operator precedence for hist triggers expression
Date: Wed, 20 Oct 2021 09:22:24 -0700 [thread overview]
Message-ID: <CAC_TJvceZ=+QoRM2Qt4uRtikG5WZ_+KEjbPreg3ss=OOHFV7QA@mail.gmail.com> (raw)
In-Reply-To: <20211020114805.3fbb7d94@gandalf.local.home>
On Wed, Oct 20, 2021 at 8:48 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> 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.
I think we achieve something like this by propagating up the
HIST_FIELD_FL_CONST flag. Thanks for the suggestions. I'll update this
in the next version.
Thanks,
Kalesh
>
> -- Steve
next prev parent reply other threads:[~2021-10-20 16:22 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
2021-10-20 16:11 ` Kalesh Singh
2021-10-20 16:19 ` Steven Rostedt
2021-10-20 16:22 ` Kalesh Singh [this message]
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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