build: add per stage build time profiling

Set BUILD_TIME_LOG=<file> to record a begin and an end event for every
prepare, configure, compile and install stage of every tool, toolchain
component, kernel and package. scripts/build-time-report.pl turns the log
into a report.

The report divides each second of the build between the stages that run
in it, so the numbers show which stages hold up the wall clock rather
than which ones burn the most CPU. Nothing is recorded and no extra
process runs when BUILD_TIME_LOG is unset.

Signed-off-by: John Crispin <john@phrozen.org>

include/host-build.mk

@@ -182,34 +182,42 @@ ifndef DUMP
   $(if $(DUMP),,$(call HostHost/Autoclean))
 
   $(HOST_STAMP_PREPARED):
+	$(call BuildTimeLog,begin,prepare)
 	@-rm -rf $(HOST_BUILD_DIR)
 	@mkdir -p $(HOST_BUILD_DIR)
 	$(foreach hook,$(Hooks/HostPrepare/Pre),$(call $(hook))$(sep))
 	$(call Host/Prepare)
 	$(foreach hook,$(Hooks/HostPrepare/Post),$(call $(hook))$(sep))
 	touch $$@
+	$(call BuildTimeLog,end,prepare)
 
   $(call Host/Exports,$(HOST_STAMP_CONFIGURED))
   $(HOST_STAMP_CONFIGURED): $(HOST_STAMP_PREPARED)
+	$(call BuildTimeLog,begin,configure)
 	$(foreach hook,$(Hooks/HostConfigure/Pre),$(call $(hook))$(sep))
 	$(call Host/Configure)
 	$(foreach hook,$(Hooks/HostConfigure/Post),$(call $(hook))$(sep))
 	touch $$@
+	$(call BuildTimeLog,end,configure)
 
   $(call Host/Exports,$(HOST_STAMP_BUILT))
   $(HOST_STAMP_BUILT): $(HOST_STAMP_CONFIGURED)
+		$(call BuildTimeLog,begin,compile)
 		$(foreach hook,$(Hooks/HostCompile/Pre),$(call $(hook))$(sep))
 		$(call Host/Compile)
 		$(foreach hook,$(Hooks/HostCompile/Post),$(call $(hook))$(sep))
 		touch $$@
+		$(call BuildTimeLog,end,compile)
 
   $(call Host/Exports,$(HOST_STAMP_INSTALLED))
   $(HOST_STAMP_INSTALLED): $(HOST_STAMP_BUILT) $(if $(FORCE_HOST_INSTALL),FORCE)
+		$(call BuildTimeLog,begin,install)
 		$(call Host/Install,$(HOST_BUILD_PREFIX))
 		$(foreach hook,$(Hooks/HostInstall/Post),$(call $(hook))$(sep))
 		mkdir -p $$(shell dirname $$@)
 		touch $(HOST_STAMP_BUILT)
 		touch $$@ $(HOST_STAMP_PROGRAMS)
+		$(call BuildTimeLog,end,install)
 
   $(call DefaultTargets,$(patsubst %,host-%,$(DEFAULT_SUBDIR_TARGETS)))
   ifndef STAMP_BUILT

include/kernel-build.mk

@@ -90,12 +90,15 @@ define BuildKernel
 
   $(Kernel/Autoclean)
   $(STAMP_PREPARED): $(if $(LINUX_SITE),$(DL_DIR)/$(LINUX_SOURCE))
+	$(call BuildTimeLog,begin,prepare)
 	-rm -rf $(KERNEL_BUILD_DIR)
 	-mkdir -p $(KERNEL_BUILD_DIR)
 	$(Kernel/Prepare)
 	touch $$@
+	$(call BuildTimeLog,end,prepare)
 
   $(KERNEL_BUILD_DIR)/symtab.h: FORCE
+	$(call BuildTimeLog,begin,compile)
 	rm -f $(KERNEL_BUILD_DIR)/symtab.h
 	touch $(KERNEL_BUILD_DIR)/symtab.h
 	+$(KERNEL_MAKE) vmlinux
@@ -124,26 +127,33 @@ define BuildKernel
 			awk '{print "*(___ksymtab_gpl+" $$$$1 ") \\" }'; \
 		echo; \
 	) > $$@
+	$(call BuildTimeLog,end,compile)
 
   $(STAMP_CONFIGURED): $(STAMP_PREPARED) $(LINUX_KCONFIG_LIST) $(TOPDIR)/.config FORCE
+	$(call BuildTimeLog,begin,configure)
 	$(Kernel/Configure)
 	touch $$@
+	$(call BuildTimeLog,end,configure)
 
   $(LINUX_DIR)/.modules: export STAGING_PREFIX=$$(STAGING_DIR_HOST)
   $(LINUX_DIR)/.modules: export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.modules: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.modules: export FAIL_ON_UNCONFIGURED=1
   $(LINUX_DIR)/.modules: $(STAMP_CONFIGURED) $(LINUX_DIR)/.config FORCE
+	$(call BuildTimeLog,begin,compile)
 	$(Kernel/CompileModules)
 	touch $$@
+	$(call BuildTimeLog,end,compile)
 
   $(LINUX_DIR)/.image: export STAGING_PREFIX=$$(STAGING_DIR_HOST)
   $(LINUX_DIR)/.image: export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.image: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.image: $(STAMP_CONFIGURED) $(if $(CONFIG_STRIP_KERNEL_EXPORTS),$(KERNEL_BUILD_DIR)/symtab.h) FORCE
+	$(call BuildTimeLog,begin,compile)
 	$(Kernel/CompileImage)
 	$(Kernel/CollectDebug)
 	touch $$@
+	$(call BuildTimeLog,end,compile)
 	
   mostlyclean: FORCE
 	$(Kernel/Clean)

include/package.mk

@@ -247,6 +247,7 @@ define Build/CoreTargets
 
   $(STAMP_PREPARED) : export PATH=$$(TARGET_PATH_PKG)
   $(STAMP_PREPARED): $(STAMP_PREPARED_DEPENDS)
+	$(call BuildTimeLog,begin,prepare)
 	@-rm -rf $(PKG_BUILD_DIR)
 	@mkdir -p $(PKG_BUILD_DIR)
 	touch $$@_check
@@ -254,18 +255,22 @@ define Build/CoreTargets
 	$(Build/Prepare)
 	$(foreach hook,$(Hooks/Prepare/Post),$(call $(hook))$(sep))
 	touch $$@
+	$(call BuildTimeLog,end,prepare)
 
   $(call Build/Exports,$(STAMP_CONFIGURED))
   $(STAMP_CONFIGURED): $(STAMP_PREPARED) $(STAMP_CONFIGURED_DEPENDS)
+	$(call BuildTimeLog,begin,configure)
 	rm -f $(STAMP_CONFIGURED_WILDCARD)
 	$(CleanStaging)
 	$(foreach hook,$(Hooks/Configure/Pre),$(call $(hook))$(sep))
 	$(Build/Configure)
 	$(foreach hook,$(Hooks/Configure/Post),$(call $(hook))$(sep))
 	touch $$@
+	$(call BuildTimeLog,end,configure)
 
   $(call Build/Exports,$(STAMP_BUILT))
   $(STAMP_BUILT): $(STAMP_CONFIGURED) $(STAMP_BUILT_DEPENDS)
+	$(call BuildTimeLog,begin,compile)
 	rm -f $$@
 	touch $$@_check
 	$(foreach hook,$(Hooks/Compile/Pre),$(call $(hook))$(sep))
@@ -274,9 +279,11 @@ define Build/CoreTargets
 	$(Build/Install)
 	$(foreach hook,$(Hooks/Install/Post),$(call $(hook))$(sep))
 	touch $$@
+	$(call BuildTimeLog,end,compile)
 
   $(STAMP_INSTALLED) : export PATH=$$(TARGET_PATH_PKG)
   $(STAMP_INSTALLED): $(STAMP_BUILT)
+	$(call BuildTimeLog,begin,install)
 	rm -rf $(STAGING_TMP_DIR)
 	mkdir -p $(STAGING_TMP_DIR)/host $(STAGING_DIR)/packages
 	$(foreach hook,$(Hooks/InstallDev/Pre),\
@@ -300,6 +307,7 @@ define Build/CoreTargets
 	fi
 	rm -rf $(STAGING_TMP_DIR)
 	touch $$@
+	$(call BuildTimeLog,end,install)
 
   ifdef Build/InstallDev
     $(_pkg_target)compile: $(STAMP_INSTALLED)

rules.mk

@@ -196,6 +196,16 @@ STAGING_DIR_IMAGE:=$(STAGING_DIR)/image
 BUILD_LOG_DIR:=$(if $(call qstrip,$(CONFIG_BUILD_LOG_DIR)),$(call qstrip,$(CONFIG_BUILD_LOG_DIR)),$(TOPDIR)/logs)
 PKG_INFO_DIR := $(STAGING_DIR)/pkginfo
 
+# Set BUILD_TIME_LOG=<file> in the environment to record a begin and an end
+# event for every prepare, configure, compile and install stage. Turn the log
+# into a report with scripts/build-time-report.pl.
+ifneq ($(BUILD_TIME_LOG),)
+  BUILD_TIME_LOG_FILE:=$(if $(filter /%,$(BUILD_TIME_LOG)),$(BUILD_TIME_LOG),$(TOPDIR)/$(BUILD_TIME_LOG))
+  BuildTimeLog = @$(SCRIPT_DIR)/build-time-log.sh $(BUILD_TIME_LOG_FILE) $(1) $(2) "$(if $(BUILD_SUBDIR),$(BUILD_SUBDIR),$(CURDIR))$(if $(BUILD_VARIANT),/$(BUILD_VARIANT))"
+else
+  BuildTimeLog =
+endif
+
 BUILD_DIR_HOST:=$(if $(IS_PACKAGE_BUILD),$(BUILD_DIR_BASE)/hostpkg,$(BUILD_DIR_BASE)/host)
 STAGING_DIR_HOST:=$(abspath $(STAGING_DIR)/../host)
 STAGING_DIR_HOSTPKG:=$(abspath $(STAGING_DIR)/../hostpkg)

scripts/build-time-log.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+#
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Records one build stage event. See scripts/build-time-report.pl.
+#
+# Usage: build-time-log.sh <logfile> <begin|end> <stage> <name>
+
+[ $# -eq 4 ] || exit 0
+
+now=$(date +%s.%N 2>/dev/null)
+case "$now" in
+	''|*N*) now=$(date +%s) ;;
+esac
+
+printf '%s\t%s\t%s\t%s\n' "$now" "$2" "$3" "$4" >> "$1" 2>/dev/null
+
+exit 0

scripts/build-time-report.pl

@@ -0,0 +1,181 @@
+#!/usr/bin/env perl
+#
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Turns a BUILD_TIME_LOG file into a report.
+#
+# Usage: build-time-report.pl [-n <count>] [-s <stage>] <logfile>
+#
+# Wall share is the share of the build duration that a stage is responsible
+# for. Each second of the build is divided between the stages that run in it,
+# so the wall shares of all stages add up to the busy time. A stage that runs
+# alone on an idle machine gets the whole second. Solo time counts only the
+# seconds in which a stage is the one thing that runs, so it is the part of
+# the build that a faster stage shortens directly.
+
+use strict;
+use warnings;
+
+my $top = 20;
+my $only_stage;
+
+while (@ARGV && $ARGV[0] =~ /^-/) {
+	my $opt = shift @ARGV;
+	if ($opt eq '-n') { $top = shift @ARGV }
+	elsif ($opt eq '-s') { $only_stage = shift @ARGV }
+	else { die "Usage: $0 [-n <count>] [-s <stage>] <logfile>\n" }
+}
+
+my $file = shift @ARGV or die "Usage: $0 [-n <count>] [-s <stage>] <logfile>\n";
+
+open(my $fh, '<', $file) or die "$0: cannot read $file: $!\n";
+
+my (@iv, %pending);
+
+while (my $line = <$fh>) {
+	chomp $line;
+	my ($time, $event, $stage, $name) = split(/\t/, $line, 4);
+	next unless defined $name;
+	next unless defined $time && $time =~ /^[0-9]+(\.[0-9]+)?$/;
+	next if defined $only_stage && $stage ne $only_stage;
+
+	my $key = "$stage\t$name";
+
+	if ($event eq 'begin') {
+		push @{$pending{$key}}, $time;
+		next;
+	}
+
+	next unless $event eq 'end';
+	my $start = $pending{$key} ? pop @{$pending{$key}} : undef;
+	next unless defined $start;
+
+	push @iv, {
+		idx => scalar @iv,
+		start => $start,
+		end => $time,
+		dur => $time - $start,
+		stage => $stage,
+		name => $name,
+		share => 0,
+		solo => 0,
+	};
+}
+
+close($fh);
+
+my $incomplete = 0;
+$incomplete += scalar @{$pending{$_}} for keys %pending;
+
+die "$0: no completed stages in $file\n" unless @iv;
+
+my @events;
+for my $iv (@iv) {
+	push @events, [ $iv->{start}, 1, $iv ];
+	push @events, [ $iv->{end}, 0, $iv ];
+}
+
+# An end event sorts before a begin event at the same instant. One stage that
+# hands over to the next one must not look like parallel work.
+@events = sort { $a->[0] <=> $b->[0] || $a->[1] <=> $b->[1] } @events;
+
+my (%active, $idle, $busy);
+$idle = 0;
+$busy = 0;
+
+my $prev = $events[0][0];
+
+for my $ev (@events) {
+	my ($t, $is_start, $iv) = @$ev;
+	my $dt = $t - $prev;
+
+	if ($dt > 0) {
+		my @cur = values %active;
+		my $n = scalar @cur;
+
+		if (!$n) {
+			$idle += $dt;
+		}
+		else {
+			$busy += $dt;
+			my $part = $dt / $n;
+			$_->{share} += $part for @cur;
+			$cur[0]->{solo} += $dt if $n == 1;
+		}
+	}
+
+	if ($is_start) { $active{$iv->{idx}} = $iv }
+	else { delete $active{$iv->{idx}} }
+
+	$prev = $t;
+}
+
+my $total = $events[-1][0] - $events[0][0];
+my $sum_dur = 0;
+$sum_dur += $_->{dur} for @iv;
+
+my (%st, %pkg);
+
+for my $iv (@iv) {
+	my $s = $st{$iv->{stage}} ||= { count => 0, dur => 0, share => 0, solo => 0 };
+	$s->{count}++;
+	$s->{dur} += $iv->{dur};
+	$s->{share} += $iv->{share};
+	$s->{solo} += $iv->{solo};
+
+	my $key = sprintf("%s [%s]", $iv->{name}, $iv->{stage});
+	my $p = $pkg{$key} ||= { dur => 0, share => 0, solo => 0 };
+	$p->{dur} += $iv->{dur};
+	$p->{share} += $iv->{share};
+	$p->{solo} += $iv->{solo};
+}
+
+sub hms {
+	my $s = shift;
+	return sprintf("%d:%02d:%05.2f",
+		int($s / 3600), int($s / 60) % 60, $s - 60 * int($s / 60));
+}
+
+sub pct {
+	my ($a, $b) = @_;
+	return $b > 0 ? 100 * $a / $b : 0;
+}
+
+printf "build window      %s\n", hms($total);
+printf "busy              %s (%.1f%%)\n", hms($busy), pct($busy, $total);
+printf "idle              %s (%.1f%%)\n", hms($idle), pct($idle, $total);
+printf "stage time        %s\n", hms($sum_dur);
+printf "mean parallelism  %.2f\n", $busy > 0 ? $sum_dur / $busy : 0;
+printf "stages completed  %d\n", scalar @iv;
+printf "stages unfinished %d\n", $incomplete if $incomplete;
+print "\n";
+
+printf "%-10s %6s %12s %12s %8s %12s %8s\n",
+	'stage', 'count', 'sum', 'wall share', 'of wall', 'solo', 'of wall';
+
+for my $name (sort { $st{$b}{share} <=> $st{$a}{share} } keys %st) {
+	my $s = $st{$name};
+	printf "%-10s %6d %12s %12s %7.1f%% %12s %7.1f%%\n",
+		$name, $s->{count}, hms($s->{dur}), hms($s->{share}),
+		pct($s->{share}, $total), hms($s->{solo}), pct($s->{solo}, $total);
+}
+
+sub table {
+	my ($title, $key, $ref) = @_;
+
+	print "\n$title\n";
+	printf "%-56s %12s %12s %12s\n", 'stage', 'duration', 'wall share', 'solo';
+
+	my @k = sort { $ref->{$b}{$key} <=> $ref->{$a}{$key} } keys %$ref;
+	splice(@k, $top) if @k > $top;
+
+	for my $name (@k) {
+		my $e = $ref->{$name};
+		printf "%-56s %12s %12s %12s\n",
+			$name, hms($e->{dur}), hms($e->{share}), hms($e->{solo});
+	}
+}
+
+table("top $top by wall share", 'share', \%pkg);
+table("top $top by solo time", 'solo', \%pkg);
+table("top $top by duration", 'dur', \%pkg);