From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 76CD92DBF75; Sat, 12 Sep 2026 12:04:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789214642; cv=none; b=UQdMaModHX5dheIOhL3etmVuX5Wx/RSuH6MBQfEIAGcXSXctHmss/fKbF/dMXf2q57dD4xbdiEZk/P7Cjrk20uqC4KOivhmJA+N5gGiFUV6sWgH9Y5S0f5V4jmYWtw72NT/bQ3A0hDKBweok+qjZ/hQ6AwqOXUknTVwXTbjfcjk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789214642; c=relaxed/simple; bh=Edr0qLMkMe1Knymj3Jygyd1Yh0+6aIH3kixvKUimZ3s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=TiJEyyUiCccHqL7Cgw/8ThaN5XkLYkqLiNmMlyToCugxidOK98khJWmK/UBXISO+rANOkFMWm7oM/Knf0AsHLd3jlSX8k+4xxJbz20xOwIhJcV22jUhFIiY3r5r/006Qvu4Rj83LvcsH3mWhDlh+p60OIsJoAB3iRLIhO1lGHFU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=J5A5bda2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="J5A5bda2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2FBDC1F000FF; Sat, 12 Sep 2026 12:03:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789214641; bh=1H9JiLnsW2DphmLyredX9YDqrz9ZBJmqxG4BukcSoBk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=J5A5bda2SrweR04U1t7Ls9KiDoX9TMS1R/9hx/EMq9xbKOjsfV5eJwur/WXoOBVRK 1EVm42I8wavCQOvd3VadapA77ViwwjmpD7u7hhfU1UUQ9qDqrOMVPKvweG5MQu2+Ky LoUALnxpqUKLJ4gfAu1PcudGABVdTG+nXmVnLmZA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ian Rogers , Namhyung Kim , Sasha Levin Subject: [PATCH 6.12 0367/1376] perf tests: Fix flakiness in branch stack sampling tests Date: Sat, 12 Sep 2026 08:46:33 +0200 Message-ID: <20260912065615.729409744@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065607.535295758@linuxfoundation.org> References: <20260912065607.535295758@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ian Rogers [ Upstream commit 344d3aec164dba83a5520f23a0d46e13e904a205 ] The branch stack sampling test (test 130) runs short iteration-based workloads to verify syscall, kernel, and trap branch stack sampling. Specifically, `test_syscall()` and `test_kernel_branches()` run `perf bench syscall basic` with loop counts of 8000 and 1000, and `test_trap_eret_branches()` runs `traploop` with 1000 iterations. Because these loop limits are extremely small, the total benchmark runtimes last only a few milliseconds (or less). Under high load, virtualization, or coarse sampling conditions, PMU cycle sampling fails to capture enough samples inside the brief benchmark loops. This leads to false negatives where the script output lacks the expected syscall, kernel, or trap branch entries (e.g. "ERROR: Branches missing getppid[^ ]*/SYSCALL/"). Fix this by increasing the workload loop counts to 100,000 across all three test sections. Running 100,000 loops still finishes virtually instantaneously (less than 0.1 seconds), but generates enough iterations to guarantee robust branch stack capture. Fixes: b55878c90ab9 ("perf test: Add test for branch stack sampling") Assisted-by: Antigravity:gemini-3.1-pro Signed-off-by: Ian Rogers Signed-off-by: Namhyung Kim Signed-off-by: Sasha Levin --- tools/perf/tests/shell/test_brstack.sh | 107 +++++++++++++++---------- 1 file changed, 66 insertions(+), 41 deletions(-) diff --git a/tools/perf/tests/shell/test_brstack.sh b/tools/perf/tests/shell/test_brstack.sh index eb5837f82e390..71550e0b37baa 100755 --- a/tools/perf/tests/shell/test_brstack.sh +++ b/tools/perf/tests/shell/test_brstack.sh @@ -110,20 +110,29 @@ test_trap_eret_branches() { return fi start_err=$err - err=0 - perf record -o $TMPDIR/perf.data --branch-filter any,save_type,u,k -- \ - perf test -w traploop 1000 > "$TMPDIR/record.txt" 2>&1 - perf script -i $TMPDIR/perf.data --fields brstacksym | \ - tr ' ' '\n' > $TMPDIR/perf.script - - # BRBINF.TYPE == TRAP are mapped to PERF_BR_IRQ by the BRBE driver - check_branches "^trap_bench\+[^ ]+/[^ ]/IRQ/" - check_branches "^[^ ]+/trap_bench\+[^ ]+/ERET/" - if [ $err -eq 0 ]; then + local ret=1 + for loops in 1000 10000 100000; do + err=0 + perf record -o $TMPDIR/perf.data --branch-filter any,save_type,u,k -- \ + perf test -w traploop $loops > "$TMPDIR/record.txt" 2>&1 + perf script -i $TMPDIR/perf.data --fields brstacksym | \ + tr ' ' '\n' > $TMPDIR/perf.script + + # BRBINF.TYPE == TRAP are mapped to PERF_BR_IRQ by the BRBE driver + check_branches "^trap_bench\+[^ ]+/[^ ]/IRQ/" + check_branches "^[^ ]+/trap_bench\+[^ ]+/ERET/" + if [ $err -eq 0 ]; then + ret=0 + break + fi + done + + if [ $ret -eq 0 ]; then echo "Testing trap & eret branches [Passed]" err=$start_err else echo "Testing trap & eret branches [Failed]" + err=1 fi } @@ -135,32 +144,40 @@ test_kernel_branches() { return fi start_err=$err - err=0 - perf record -o $TMPDIR/perf.data --branch-filter any,k -- \ - perf bench syscall basic --loop 1000 > "$TMPDIR/record.txt" 2>&1 - perf script -i $TMPDIR/perf.data --fields brstack | \ - tr ' ' '\n' > $TMPDIR/perf.script - - # Example of branch entries: - # "0xffffffff93bda241/0xffffffff93bda20f/M/-/-/..." - # Source addresses come first in user or kernel code. Next is the target - # address that must be in the kernel. - - # Look for source addresses with top bit set - if ! grep -q -E -m1 "^0x[89a-f][0-9a-f]{15}" $TMPDIR/perf.script; then - echo "Testing kernel branch sampling [Failed kernel branches missing]" - err=1 - fi - # Look for no target addresses without top bit set - if grep -q -E -m1 "^0x[0-9a-f]{0,16}/0x[0-7][0-9a-f]{1,15}/" $TMPDIR/perf.script; then - echo "Testing kernel branch sampling [Failed user branches found]" - err=1 - fi - if [ $err -eq 0 ]; then + local ret=1 + for loops in 1000 10000 100000; do + err=0 + perf record -o $TMPDIR/perf.data --branch-filter any,k -- \ + perf bench syscall basic --loop $loops > "$TMPDIR/record.txt" 2>&1 + perf script -i $TMPDIR/perf.data --fields brstack | \ + tr ' ' '\n' > $TMPDIR/perf.script + + # Example of branch entries: + # "0xffffffff93bda241/0xffffffff93bda20f/M/-/-/..." + # Source addresses come first in user or kernel code. Next is the target + # address that must be in the kernel. + + # Look for source addresses with top bit set + if ! grep -q -E -m1 "^0x[89a-f][0-9a-f]{15}" $TMPDIR/perf.script; then + err=1 + fi + # Look for no target addresses without top bit set + if grep -q -E -m1 "^0x[0-9a-f]{0,16}/0x[0-7][0-9a-f]{1,15}/" \ + $TMPDIR/perf.script; then + err=1 + fi + if [ $err -eq 0 ]; then + ret=0 + break + fi + done + + if [ $ret -eq 0 ]; then echo "Testing kernel branch sampling [Passed]" err=$start_err else echo "Testing kernel branch sampling [Failed]" + err=1 fi } @@ -206,20 +223,28 @@ test_syscall() { return fi start_err=$err - err=0 - perf record -o $TMPDIR/perf.data --branch-filter \ - any_call,save_type,u,k -c 10007 -- \ - perf bench syscall basic --loop 8000 > "$TMPDIR/record.txt" 2>&1 - perf script -i $TMPDIR/perf.data --fields brstacksym | \ - tr ' ' '\n' > $TMPDIR/perf.script - - check_branches "getppid[^ ]*/SYSCALL/" + local ret=1 + for loops in 8000 30000 100000; do + err=0 + perf record -o $TMPDIR/perf.data --branch-filter \ + any_call,save_type,u,k -c 10007 -- \ + perf bench syscall basic --loop $loops > "$TMPDIR/record.txt" 2>&1 + perf script -i $TMPDIR/perf.data --fields brstacksym | \ + tr ' ' '\n' > $TMPDIR/perf.script + + check_branches "getppid[^ ]*/SYSCALL/" + if [ $err -eq 0 ]; then + ret=0 + break + fi + done - if [ $err -eq 0 ]; then + if [ $ret -eq 0 ]; then echo "Testing syscalls [Passed]" err=$start_err else echo "Testing syscalls [Failed]" + err=1 fi } set -e -- 2.53.0