On 1/23/23 14:02, Naveen N. Rao wrote:
> BPF filtering tests can sometime fail. Running the test in verbose mode
> shows the following:
> $ sudo perf test 42
> 42: BPF filter :
> 42.1: Basic BPF filtering : FAILED!
> 42.2: BPF pinning : Skip
> 42.3: BPF prologue generation : Skip
> $ perf --version
> perf version 4.18.0-425.3.1.el8.ppc64le
> $ sudo perf test -v 42
> 42: BPF filter :
> 42.1: Basic BPF filtering :
> --- start ---
> test child forked, pid 711060
> ...
> bpf: config 'func=do_epoll_wait' is ok
> Looking at the vmlinux_path (8 entries long)
> Using /usr/lib/debug/lib/modules/4.18.0-425.3.1.el8.ppc64le/vmlinux for symbols
> Open Debuginfo file: /usr/lib/debug/.build-id/81/56f5a07f92ccb62c5600ba0e4aacfb5f3a7534.debug
> Try to find probe point from debuginfo.
> Matched function: do_epoll_wait [4ef8cb0]
> found inline addr: 0xc00000000061dbe4
> Probe point found: __se_compat_sys_epoll_pwait+196
> found inline addr: 0xc00000000061d9f4
> Probe point found: __se_sys_epoll_pwait+196
> found inline addr: 0xc00000000061d824
> Probe point found: __se_sys_epoll_wait+36
> Found 3 probe_trace_events.
> Opening /sys/kernel/tracing//kprobe_events write=1
> ...
> BPF filter result incorrect, expected 56, got 56 samples
> test child finished with -1
> ---- end ----
> BPF filter subtest 1: FAILED!
Patch looks good to me.
Reviewed-by: Kajol Jain<kjain@xxxxxxxxxxxxx>
Thanks,
Kajol Jain
>
> The statement above about the result being incorrect looks weird, and it
> is due to that particular perf build missing commit 3e11300cdfd5f1
> ("perf test: Fix bpf test sample mismatch reporting"). In reality, due
> to commit 4b04e0decd2518 ("perf test: Fix basic bpf filtering test"),
> perf expects there to be 56*3 samples.
>
> However, the number of samples we receive is going to be dependent on
> where the probes are installed, which is dependent on where
> do_epoll_wait gets inlined. On s390x, it looks like probes at all the
> inlined locations are hit. But, that is not the case on ppc64le.
>
> Fix this by switching the test to instead use the syscall tracepoint.
> This ensures that we will only ever install a single event enabling us
> to reliably determine the sample count.
>
> Reported-by: Disha Goel <disgoel@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> ---
> tools/perf/tests/bpf-script-example.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/tests/bpf-script-example.c b/tools/perf/tests/bpf-script-example.c
> index 7981c69ed1b456..b638cc99d5ae56 100644
> --- a/tools/perf/tests/bpf-script-example.c
> +++ b/tools/perf/tests/bpf-script-example.c
> @@ -43,7 +43,7 @@ struct {
> __type(value, int);
> } flip_table SEC(".maps");
>
> -SEC("func=do_epoll_wait")
> +SEC("syscalls:sys_enter_epoll_pwait")
> int bpf_func__SyS_epoll_pwait(void *ctx)
> {
> int ind =0;
>
> base-commit: 5670ebf54bd26482f57a094c53bdc562c106e0a9
