From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS53758 23.128.96.0/24 X-Spam-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id E9E2D1F953 for ; Wed, 17 Nov 2021 09:41:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235400AbhKQJoK (ORCPT ); Wed, 17 Nov 2021 04:44:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235401AbhKQJnx (ORCPT ); Wed, 17 Nov 2021 04:43:53 -0500 Received: from vuizook.err.no (vuizook.err.no [IPv6:2a02:20c8:2640::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C9A8C061220 for ; Wed, 17 Nov 2021 01:40:04 -0800 (PST) Received: from [2400:4160:1877:2b00:29f9:f15d:e50b:8944] (helo=glandium.org) by vuizook.err.no with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mnHQ3-006OmA-8Y; Wed, 17 Nov 2021 09:39:58 +0000 Received: from glandium by goemon.lan with local (Exim 4.94.2) (envelope-from ) id 1mnHPv-009v09-Pg; Wed, 17 Nov 2021 18:39:47 +0900 Date: Wed, 17 Nov 2021 18:39:47 +0900 From: Mike Hommey To: =?utf-8?B?w4Z2YXIgQXJuZmrDtnLDsA==?= Bjarmason Cc: git@vger.kernel.org, Junio C Hamano , Phillip Wood , Jeff King , Dan Jacques , Eric Wong , Jonathan Nieder Subject: Re: [PATCH v3 18/23] Makefiles: add and use wildcard "mkdir -p" template Message-ID: <20211117093947.ifkrvddmiiu3hg2v@glandium.org> X-GPG-Fingerprint: 182E 161D 1130 B9FC CD7D B167 E42A A04F A6AA 8C72 References: <20211117025148.awdha4udu5kmzwbe@glandium.org> <211117.86wnl76sal.gmgdl@evledraar.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <211117.86wnl76sal.gmgdl@evledraar.gmail.com> Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Wed, Nov 17, 2021 at 10:26:27AM +0100, Ævar Arnfjörð Bjarmason wrote: > > On Wed, Nov 17 2021, Mike Hommey wrote: > > > On Tue, Nov 16, 2021 at 01:00:18PM +0100, Ævar Arnfjörð Bjarmason wrote: > >> Add a template to do the "mkdir -p" of $(@D) (the parent dir of $@) > >> for us, and use it for the "make lint-docs" targets I added in > >> 8650c6298c1 (doc lint: make "lint-docs" non-.PHONY, 2021-10-15). > >> > >> As seen in 4c64fb5aad9 (Documentation/Makefile: fix lint-docs mkdir > >> dependency, 2021-10-26) maintaining these manual lists of parent > >> directory dependencies is fragile, in addition to being obviously > >> verbose. > >> > >> I used this pattern at the time because I couldn't find another method > >> than "order-only" prerequisites to avoid doing a "mkdir -p $(@D)" for > >> every file being created, which as noted in [1] would be significantly > >> slower. > >> > >> But as it turns out we can use this neat trick of only doing a "mkdir > >> -p" if the $(wildcard) macro tells us the path doesn't exist. A re-run > >> of a performance test similar to thatnoted downthread of [1] in [2] > >> shows that this is faster, in addition to being less verbose and more > >> reliable (this uses my "git-hyperfine" thin wrapper for "hyperfine"[3]): > >> > >> $ git hyperfine -L rev HEAD~0,HEAD~1 -b 'make -C Documentation lint-docs' -p 'rm -rf Documentation/.build' 'make -C Documentation lint-docs' > >> Benchmark 1: make -C Documentation lint-docs' in 'HEAD~0 > >> Time (mean ± σ): 2.129 s ± 0.011 s [User: 1.840 s, System: 0.321 s] > >> Range (min … max): 2.121 s … 2.158 s 10 runs > >> > >> Benchmark 2: make -C Documentation lint-docs' in 'HEAD~1 > >> Time (mean ± σ): 2.659 s ± 0.002 s [User: 2.306 s, System: 0.397 s] > >> Range (min … max): 2.657 s … 2.662 s 10 runs > >> > >> Summary > >> 'make -C Documentation lint-docs' in 'HEAD~0' ran > >> 1.25 ± 0.01 times faster than 'make -C Documentation lint-docs' in 'HEAD~1' > >> > >> So let's use that pattern both for the "lint-docs" target, and a few > >> miscellaneous other targets. > >> > >> This method of creating parent directories is explicitly racy in that > >> we don't know if we're going to say always create a "foo" followed by > >> a "foo/bar" under parallelism, or skip the "foo" because we created > >> "foo/bar" first. In this case it doesn't matter for anything except > >> that we aren't guaranteed to get the same number of rules firing when > >> running make in parallel. > > > > Something else that is racy is that $(wildcard) might be saying the > > directory doesn't exist while there's another make subprocess that has > > already started spawning `mkdir -p` for that directory. > > That doesn't make a huge difference, but you can probably still end up > > with multiple `mkdir -p` runs for the same directory. > > > > I think something like the following could work while avoiding those > > races: > > > > define create_parent_dir_RULE > > $(1): | $(dir $(1)). > > ALL_DIRS += $(dir $(1)) > > endef > > > > define create_parent_dir_TARGET > > $(1)/.: $(dir $(1)). > > echo mkdir $$(@D) erf, s/echo // > > endef > > > > $(eval $(call create_parent_dir_RULE, first/path/file)) > > $(eval $(call create_parent_dir_RULE, second/path/file)) > > # ... > > > > $(foreach dir,$(sort $(ALL_DIRS)),$(eval $(call create_parent_dir_TARGET,$(dir:%/=%)))) > > I think the "race" just isn't a problem, and makes managing this much > simpler. > > I.e. we already rely on "mkdir -p" not failing on an existing directory, > so the case where we redundantly try to create a directory that just got > created by a concurrent process is OK, and as the quoted benchmark shows > is much faster than a similar (but not quite the same as) a > dependency-based implementaiton. > > I haven't implemented your solution, but it seems to be inherently more > complex. > > I.e. with the one I've got you just stick the "mkdir if needed" > one-liner in each rule, with yours you'll need to accumulate things in > ALL_DIRS, and have some foreach somewhere or dependency relationship to > create those beforehand if they're nested, no? For each rule, it would also be a oneliner to add above the rule. The rest would be a prelude and a an epilogue to stick somewhere in the Makefile.