Re: [PATCH v3] perf test: Fixes for check branch stack sampling

[Ian Rogers]

On Sat, Aug 8, 2026 at 9:16 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> When filtering branch stack samples on user events they sample in user
> land but may have come from the kernel. Avoid the target address being
> a kernel address but allow the source to be the kernel.
>
> When filtering branch stack samples on kernel events they sample in
> kernel land but may have come from user land. Avoid the target being a
> user address but allow the source to be in user land.
>
> Increase the duration of the system call sampling test to make the
> likelihood of sampling a system call higher (increased from 1000 to
> 8000 loops - a number found through experimentation on an Intel
> Tigerlake laptop), also make the period of the event a prime number.
>
> Put unneeded perf record output into a temporary file so that the test
> output isn't cluttered. More clearly state which test is running and
> the pass, fail or skipped result of the test.
>
> These changes make the test on an Intel tigerlake laptop reliably pass
> rather than reliably fail.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

Sorry, sent in error. This change is already merged.

Thanks,
Ian

> ---
>  tools/perf/tests/shell/test_brstack.sh | 134 ++++++++++++++++---------
>  1 file changed, 84 insertions(+), 50 deletions(-)
>
> diff --git a/tools/perf/tests/shell/test_brstack.sh b/tools/perf/tests/shell/test_brstack.sh
> index 85233d435be6..025ed9d3d110 100755
> --- a/tools/perf/tests/shell/test_brstack.sh
> +++ b/tools/perf/tests/shell/test_brstack.sh
> @@ -40,7 +40,7 @@ is_arm64() {
>
>  check_branches() {
>         if ! tr -s ' ' '\n' < "$TMPDIR/perf.script" | grep -E -m1 -q "$1"; then
> -               echo "Branches missing $1"
> +               echo "ERROR: Branches missing $1"
>                 err=1
>         fi
>  }
> @@ -48,6 +48,8 @@ check_branches() {
>  test_user_branches() {
>         echo "Testing user branch stack sampling"
>
> +       start_err=$err
> +       err=0
>         perf record -o "$TMPDIR/perf.data" --branch-filter any,save_type,u -- ${TESTPROG} > "$TMPDIR/record.txt" 2>&1
>         perf script -i "$TMPDIR/perf.data" --fields brstacksym > "$TMPDIR/perf.script"
>
> @@ -73,59 +75,80 @@ test_user_branches() {
>         perf script -i "$TMPDIR/perf.data" --fields brstack | \
>                 tr ' ' '\n' > "$TMPDIR/perf.script"
>
> -       # There should be no kernel addresses with the u option, in either
> -       # source or target addresses.
> -       if grep -E -m1 "0x[89a-f][0-9a-f]{15}" $TMPDIR/perf.script; then
> -               echo "ERROR: Kernel address found in user mode"
> +       # There should be no kernel addresses in the target with the u option.
> +       if grep -q -E -m1 "^0x[0-9a-f]{0,16}/0x[89a-f][0-9a-f]{15}/" $TMPDIR/perf.script; then
> +               echo "Testing user branch stack sampling [Failed kernel address found in user mode]"
>                 err=1
>         fi
>         # some branch types are still not being tested:
>         # IND COND_CALL COND_RET SYSRET SERROR NO_TX
> +       if [ $err -eq 0 ]; then
> +               echo "Testing user branch stack sampling [Passed]"
> +               err=$start_err
> +       else
> +               echo "Testing user branch stack sampling [Failed]"
> +       fi
>  }
>
>  test_trap_eret_branches() {
>         echo "Testing trap & eret branches"
> +
>         if ! is_arm64; then
> -               echo "skip: not arm64"
> +               echo "Testing trap & eret branches [Skipped not arm64]"
> +               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<n>.TYPE == TRAP are mapped to PERF_BR_IRQ by the BRBE driver
> +       check_branches "^trap_bench\+[^ ]+/[^ ]/IRQ/"
> +       check_branches "^[^ ]+/trap_bench\+[^ ]+/ERET/"
> +       if [ $err -eq 0 ]; then
> +               echo "Testing trap & eret branches [Passed]"
> +               err=$start_err
>         else
> -               perf record -o $TMPDIR/perf.data --branch-filter any,save_type,u,k -- \
> -                       perf test -w traploop 1000
> -               perf script -i $TMPDIR/perf.data --fields brstacksym | \
> -                       tr ' ' '\n' > $TMPDIR/perf.script
> -
> -               # BRBINF<n>.TYPE == TRAP are mapped to PERF_BR_IRQ by the BRBE driver
> -               check_branches "^trap_bench\+[^ ]+/[^ ]/IRQ/"
> -               check_branches "^[^ ]+/trap_bench\+[^ ]+/ERET/"
> +               echo "Testing trap & eret branches [Failed]"
>         fi
>  }
>
>  test_kernel_branches() {
> -       echo "Testing that k option only includes kernel source addresses"
> +       echo "Testing kernel branch sampling"
>
> -       if ! perf record --branch-filter any,k -o- -- true > /dev/null; then
> -               echo "skip: not enough privileges"
> +       if ! perf record --branch-filter any,k -o- -- true > "$TMPDIR/record.txt" 2>&1; then
> +               echo "Testing that k option [Skipped not enough privileges]"
> +               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]{0,15}/" $TMPDIR/perf.script; then
> +               echo "Testing kernel branch sampling [Failed user branches found]"
> +               err=1
> +       fi
> +       if [ $err -eq 0 ]; then
> +               echo "Testing kernel branch sampling [Passed]"
> +               err=$start_err
>         else
> -               perf record -o $TMPDIR/perf.data --branch-filter any,k -- \
> -                       perf bench syscall basic --loop 1000
> -               perf script -i $TMPDIR/perf.data --fields brstack | \
> -                       tr ' ' '\n' > $TMPDIR/perf.script
> -
> -               # Example of branch entries:
> -               #       "0xffffffff93bda241/0xffffffff93bda20f/M/-/-/..."
> -               # Source addresses come first and target address can be either
> -               # userspace or kernel even with k option, as long as the source
> -               # is in kernel.
> -
> -               #Look for source addresses with top bit set
> -               if ! grep -E -m1 "^0x[89a-f][0-9a-f]{15}" $TMPDIR/perf.script; then
> -                       echo "ERROR: Kernel branches missing"
> -                       err=1
> -               fi
> -               # Look for no source addresses without top bit set
> -               if grep -E -m1 "^0x[0-7][0-9a-f]{0,15}" $TMPDIR/perf.script; then
> -                       echo "ERROR: User branches found with kernel filter"
> -                       err=1
> -               fi
> +               echo "Testing kernel branch sampling [Failed]"
>         fi
>  }
>
> @@ -136,14 +159,15 @@ test_filter() {
>         test_filter_expect=$2
>
>         echo "Testing branch stack filtering permutation ($test_filter_filter,$test_filter_expect)"
> -       perf record -o "$TMPDIR/perf.data" --branch-filter "$test_filter_filter,save_type,u" -- ${TESTPROG}  > "$TMPDIR/record.txt" 2>&1
> +       perf record -o "$TMPDIR/perf.data" --branch-filter "$test_filter_filter,save_type,u" -- \
> +               ${TESTPROG}  > "$TMPDIR/record.txt" 2>&1
>         perf script -i "$TMPDIR/perf.data" --fields brstack > "$TMPDIR/perf.script"
>
>         # fail if we find any branch type that doesn't match any of the expected ones
>         # also consider UNKNOWN branch types (-)
>         if [ ! -s "$TMPDIR/perf.script" ]
>         then
> -               echo "Empty script output"
> +               echo "Testing branch stack filtering [Failed empty script output]"
>                 err=1
>                 return
>         fi
> @@ -154,26 +178,36 @@ test_filter() {
>           > "$TMPDIR/perf.script-filtered" || true
>         if [ -s "$TMPDIR/perf.script-filtered" ]
>         then
> -               echo "Unexpected branch filter in script output"
> +               echo "Testing branch stack filtering [Failed unexpected branch filter]"
>                 cat "$TMPDIR/perf.script"
>                 err=1
>                 return
>         fi
> +       echo "Testing branch stack filtering [Passed]"
>  }
>
>  test_syscall() {
>         echo "Testing syscalls"
>         # skip if perf doesn't have enough privileges
> -       if ! perf record --branch-filter any,k -o- -- true > /dev/null; then
> -               echo "skip: not enough privileges"
> +       if ! perf record --branch-filter any,k -o- -- true > "$TMPDIR/record.txt" 2>&1; then
> +               echo "Testing syscalls [Skipped: not enough privileges]"
> +               return
> +       fi
> +       start_err=$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/"
> +
> +       if [ $err -eq 0 ]; then
> +               echo "Testing syscalls [Passed]"
> +               err=$start_err
>         else
> -               perf record -o $TMPDIR/perf.data --branch-filter \
> -                       any_call,save_type,u,k -c 10000 -- \
> -                       perf bench syscall basic --loop 1000
> -               perf script -i $TMPDIR/perf.data --fields brstacksym | \
> -                       tr ' ' '\n' > $TMPDIR/perf.script
> -
> -               check_branches "getppid[^ ]*/SYSCALL/"
> +               echo "Testing syscalls [Failed]"
>         fi
>  }
>  set -e
> --
> 2.53.0.1213.gd9a14994de-goog
>