perf test: Add a shell test for 'perf stat --bpf-counters' new option

Add a test to compare the output of perf-stat with and without option
--bpf-counters. If the difference is more than 10%, the test is considered
as failed.

Committer testing:

# perf test bpf-counters
86: perf stat --bpf-counters test : Ok
# perf test -v bpf-counters
86: perf stat --bpf-counters test :
--- start ---
test child forked, pid 2433339
test child finished with 0
---- end ----
perf stat --bpf-counters test: Ok
#

Signed-off-by: Song Liu <[e-mail]>
Requested-by: Arnaldo Carvalho de Melo <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/shell/stat_bpf_counters.sh

···
+#!/bin/sh
+# perf stat --bpf-counters test
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+
+# check whether $2 is within +/- 10% of $1
+compare_number()
+{
+       first_num=$1
+       second_num=$2
+
+       # upper bound is first_num * 110%
+       upper=$(( $first_num + $first_num / 10 ))
+       # lower bound is first_num * 90%
+       lower=$(( $first_num - $first_num / 10 ))
+
+       if [ $second_num -gt $upper ] || [ $second_num -lt $lower ]; then
+               echo "The difference between $first_num and $second_num are greater than 10%."
+               exit 1
+       fi
+}
+
+# skip if --bpf-counters is not supported
+perf stat --bpf-counters true > /dev/null 2>&1 || exit 2
+
+base_cycles=$(perf stat --no-big-num -e cycles -- perf bench sched messaging -g 1 -l 100 -t 2>&1 | awk '/cycles/ {print $1}')
+bpf_cycles=$(perf stat --no-big-num --bpf-counters -e cycles -- perf bench sched messaging -g 1 -l 100 -t 2>&1 | awk '/cycles/ {print $1}')
+
+compare_number $base_cycles $bpf_cycles
+exit 0