sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 224 insertions, 0 deletions

diff --git a/scripts/bootgraph.pl b/scripts/bootgraph.pl
new file mode 100755
index 000000000..79c903292
--- /dev/null
+++ b/scripts/bootgraph.pl
@@ -0,0 +1,224 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0-only
+
+# Copyright 2008, Intel Corporation
+#
+# This file is part of the Linux kernel
+#
+# Authors:
+# 	Arjan van de Ven <arjan@linux.intel.com>
+
+
+#
+# This script turns a dmesg output into a SVG graphic that shows which
+# functions take how much time. You can view SVG graphics with various
+# programs, including Inkscape, The Gimp and Firefox.
+#
+#
+# For this script to work, the kernel needs to be compiled with the
+# CONFIG_PRINTK_TIME configuration option enabled, and with
+# "initcall_debug" passed on the kernel command line.
+#
+# usage:
+# 	dmesg | perl scripts/bootgraph.pl > output.svg
+#
+
+use strict;
+use Getopt::Long;
+my $header = 0;
+
+sub help {
+	my $text = << "EOM";
+Usage:
+1) dmesg | perl scripts/bootgraph.pl [OPTION] > output.svg
+2) perl scripts/bootgraph.pl -h
+
+Options:
+	-header	Insert kernel version and date
+EOM
+	my $std=shift;
+	if ($std == 1) {
+		print STDERR $text;
+	} else {
+		print $text;
+	}
+	exit;
+}
+
+GetOptions(
+	'h|help'	=>\&help,
+	'header'	=>\$header
+);
+
+my %start;
+my %end;
+my %type;
+my $done = 0;
+my $maxtime = 0;
+my $firsttime = 99999;
+my $count = 0;
+my %pids;
+my %pidctr;
+
+my $headerstep = 20;
+my $xheader = 15;
+my $yheader = 25;
+my $cyheader = 0;
+
+while (<>) {
+	my $line = $_;
+	if ($line =~ /([0-9\.]+)\] calling  ([a-zA-Z0-9\_\.]+)\+/) {
+		my $func = $2;
+		if ($done == 0) {
+			$start{$func} = $1;
+			$type{$func} = 0;
+			if ($1 < $firsttime) {
+				$firsttime = $1;
+			}
+		}
+		if ($line =~ /\@ ([0-9]+)/) {
+			$pids{$func} = $1;
+		}
+		$count = $count + 1;
+	}
+
+	if ($line =~ /([0-9\.]+)\] async_waiting @ ([0-9]+)/) {
+		my $pid = $2;
+		my $func;
+		if (!defined($pidctr{$pid})) {
+			$func = "wait_" . $pid . "_1";
+			$pidctr{$pid} = 1;
+		} else {
+			$pidctr{$pid} = $pidctr{$pid} + 1;
+			$func = "wait_" . $pid . "_" . $pidctr{$pid};
+		}
+		if ($done == 0) {
+			$start{$func} = $1;
+			$type{$func} = 1;
+			if ($1 < $firsttime) {
+				$firsttime = $1;
+			}
+		}
+		$pids{$func} = $pid;
+		$count = $count + 1;
+	}
+
+	if ($line =~ /([0-9\.]+)\] initcall ([a-zA-Z0-9\_\.]+)\+.*returned/) {
+		if ($done == 0) {
+			$end{$2} = $1;
+			$maxtime = $1;
+		}
+	}
+
+	if ($line =~ /([0-9\.]+)\] async_continuing @ ([0-9]+)/) {
+		my $pid = $2;
+		my $func =  "wait_" . $pid . "_" . $pidctr{$pid};
+		$end{$func} = $1;
+		$maxtime = $1;
+	}
+	if ($line =~ /Write protecting the/) {
+		$done = 1;
+	}
+	if ($line =~ /Freeing unused kernel memory/) {
+		$done = 1;
+	}
+}
+
+if ($count == 0) {
+    print STDERR <<END;
+No data found in the dmesg. Make sure that 'printk.time=1' and
+'initcall_debug' are passed on the kernel command line.
+END
+	help(1);
+    exit 1;
+}
+
+print "<?xml version=\"1.0\" standalone=\"no\"?> \n";
+print "<svg width=\"2000\" height=\"100%\" version=\"1.1\" xmlns=\"http://www.w3.org/2000/svg\">\n";
+
+
+if ($header) {
+	my $version = `uname -a`;
+	my $date = `date`;
+	print "<text transform=\"translate($xheader,$yheader)\">Kernel version: $version</text>\n";
+	$cyheader = $yheader+$headerstep;
+	print "<text transform=\"translate($xheader,$cyheader)\">Date: $date</text>\n";
+}
+
+my @styles;
+
+$styles[0] = "fill:rgb(0,0,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[1] = "fill:rgb(0,255,0);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[2] = "fill:rgb(255,0,20);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[3] = "fill:rgb(255,255,20);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[4] = "fill:rgb(255,0,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[5] = "fill:rgb(0,255,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[6] = "fill:rgb(0,128,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[7] = "fill:rgb(0,255,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[8] = "fill:rgb(255,0,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[9] = "fill:rgb(255,255,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[10] = "fill:rgb(255,128,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[11] = "fill:rgb(128,255,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+
+my $style_wait = "fill:rgb(128,128,128);fill-opacity:0.5;stroke-width:0;stroke:rgb(0,0,0)";
+
+my $mult = 1950.0 / ($maxtime - $firsttime);
+my $threshold2 = ($maxtime - $firsttime) / 120.0;
+my $threshold = $threshold2/10;
+my $stylecounter = 0;
+my %rows;
+my $rowscount = 1;
+my @initcalls = sort { $start{$a} <=> $start{$b} } keys(%start);
+
+foreach my $key (@initcalls) {
+	my $duration = $end{$key} - $start{$key};
+
+	if ($duration >= $threshold) {
+		my ($s, $s2, $s3, $e, $w, $y, $y2, $style);
+		my $pid = $pids{$key};
+
+		if (!defined($rows{$pid})) {
+			$rows{$pid} = $rowscount;
+			$rowscount = $rowscount + 1;
+		}
+		$s = ($start{$key} - $firsttime) * $mult;
+		$s2 = $s + 6;
+		$s3 = $s + 1;
+		$e = ($end{$key} - $firsttime) * $mult;
+		$w = $e - $s;
+
+		$y = $rows{$pid} * 150;
+		$y2 = $y + 4;
+
+		$style = $styles[$stylecounter];
+		$stylecounter = $stylecounter + 1;
+		if ($stylecounter > 11) {
+			$stylecounter = 0;
+		};
+
+		if ($type{$key} == 1) {
+			$y = $y + 15;
+			print "<rect x=\"$s\" width=\"$w\" y=\"$y\" height=\"115\" style=\"$style_wait\"/>\n";
+		} else {
+			print "<rect x=\"$s\" width=\"$w\" y=\"$y\" height=\"145\" style=\"$style\"/>\n";
+			if ($duration >= $threshold2) {
+				print "<text transform=\"translate($s2,$y2) rotate(90)\">$key</text>\n";
+			} else {
+				print "<text transform=\"translate($s3,$y2) rotate(90)\" font-size=\"3pt\">$key</text>\n";
+			}
+		}
+	}
+}
+
+
+# print the time line on top
+my $time = $firsttime;
+my $step = ($maxtime - $firsttime) / 15;
+while ($time < $maxtime) {
+	my $s3 = ($time - $firsttime) * $mult;
+	my $tm = int($time * 100) / 100.0;
+	print "<text transform=\"translate($s3,89) rotate(90)\">$tm</text>\n";
+	$time = $time + $step;
+}
+
+print "</svg>\n";