Messages in this thread Patch in this message | | | Date | Wed, 22 Mar 2023 13:13:51 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH 1/2] tracing/hist: simplify contains_operator() |
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On Sat, Mar 18, 2023 at 03:12:08PM -0400, Steven Rostedt wrote: > On Thu, 2 Mar 2023 17:17:54 +0000 > Mark Rutland <mark.rutland@arm.com> wrote: > > FYI, we follow Linus's preference that subjects start with a capital > letter. Unless of course you are a socialist and dislike capitalism? > > tracing/hist: Simplify contains_operator() >
Sorry; I always get this wrong since many other trees do everything lower case (or support total commit message anarchy). I'll go fix that up.
> > > In a subsequent patch we'll add additional operators for histogram > > expressions. > > Refrain from using "subsequent patch", instead say: > > Simplify contains_operator() in order to support additional operators > for histogram expressions.
Sure.
> > > > > In preparation for adding additional operators, this patch refactors > > contains_operator() to consider each operator within a precedence group > > independently by using the 'sep' pointer as the current rightmost > > operator, and removing the separate op pointers. > > > > Within each precedence group, this allows operators to be checked > > independently with a consistent pattern: > > > > op = strrchr(str, $OP_CHAR); > > if (op > *sep) { > > *sep = op; > > field_op = $FIELD_OP_TYPE; > > } > > > > This makes it easy to add new operators of the same precedence without > > needing to check multiple pointers, and without needing a final switch > > statement to recover the relevant pointer. > > > > There should be no functional change as a result of this patch. > > > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > > Cc: Masami Hiramatsu <mhiramat@kernel.org> > > Cc: Steven Rostedt (Google) <rostedt@goodmis.org> > > Cc: Tom Zanussi <zanussi@kernel.org> > > Cc: linux-trace-kernel@vger.kernel.org > > --- > > kernel/trace/trace_events_hist.c | 80 ++++++++++++-------------------- > > 1 file changed, 30 insertions(+), 50 deletions(-) > > > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > > index 10d36f751fcd..a308da2cde2f 100644 > > --- a/kernel/trace/trace_events_hist.c > > +++ b/kernel/trace/trace_events_hist.c > > @@ -1813,13 +1813,15 @@ static char *expr_str(struct hist_field *field, unsigned int level) > > static int contains_operator(char *str, char **sep) > > { > > enum field_op_id field_op = FIELD_OP_NONE; > > - char *minus_op, *plus_op, *div_op, *mult_op; > > + char *op; > > > > + *sep = NULL; > > Hmm!
Ugh, sorry, I had completely glossed over the:
if (sep) { ... // assignments to *sep here ... }
... in the existing code.
I'll go rework that...
> > > > > /* > > - * Report the last occurrence of the operators first, so that the > > - * expression is evaluated left to right. This is important since > > - * subtraction and division are not associative. > > + * For operators of the same precedence report the last occurrence of > > + * the operators first, so that the expression is evaluated left to > > + * right. This is important since subtraction and division are not > > + * associative. > > * > > * e.g > > * 64/8/4/2 is 1, i.e 64/8/4/2 = ((64/8)/4)/2 > > @@ -1830,68 +1832,46 @@ static int contains_operator(char *str, char **sep) > > * First, find lower precedence addition and subtraction > > * since the expression will be evaluated recursively. > > */ > > - minus_op = strrchr(str, '-'); > > - if (minus_op) { > > + op = strrchr(str, '-'); > > + if (op > *sep) { > > Why compare to *sep if it is always NULL?
As in the commit message, that was just so that every check for an operator had the same shape. I can certainly drop this for the first check and just have:
op = strrchr(str, '-'); if (op) { ... }
> > Oh! But later in the code we have: > > if (contains_operator(field, NULL) || is_var_ref(field)) > > I wonder how *sep = NULL will handle that?
Yep, I got this wrong. I'll go rejig that.
Thanks, Mark.
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