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perf tests: Fix flakiness in branch stack sampling tests

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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: b55878c90a ("perf test: Add test for branch stack sampling")
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Ian Rogers 2026-06-22 18:27:54 -07:00 committed by Namhyung Kim
parent b02027776a
commit 344d3aec16
1 changed files with 62 additions and 37 deletions
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99
tools/perf/tests/shell/test_brstack.sh
View File

@ -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
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<n>.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
# BRBINF<n>.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
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.
# 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
# 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
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/"
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