From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94086C7619A for ; Wed, 22 Mar 2023 13:14:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230355AbjCVNN6 (ORCPT ); Wed, 22 Mar 2023 09:13:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229656AbjCVNN5 (ORCPT ); Wed, 22 Mar 2023 09:13:57 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C0DD419C73; Wed, 22 Mar 2023 06:13:55 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 65D864B3; Wed, 22 Mar 2023 06:14:39 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.53.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 736E03F6C4; Wed, 22 Mar 2023 06:13:54 -0700 (PDT) Date: Wed, 22 Mar 2023 13:13:51 +0000 From: Mark Rutland To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mhiramat@kernel.org, zanussi@kernel.org Subject: Re: [PATCH 1/2] tracing/hist: simplify contains_operator() Message-ID: References: <20230302171755.1821653-1-mark.rutland@arm.com> <20230302171755.1821653-2-mark.rutland@arm.com> <20230318151208.61d73823@rorschach.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230318151208.61d73823@rorschach.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 18, 2023 at 03:12:08PM -0400, Steven Rostedt wrote: > On Thu, 2 Mar 2023 17:17:54 +0000 > Mark Rutland 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 > > Cc: Masami Hiramatsu > > Cc: Steven Rostedt (Google) > > Cc: Tom Zanussi > > 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.