Messages in this thread | | | Subject | Re: [PATCH] bpf: Enable bpf support for reading branch records in powerpc | From | Daniel Borkmann <> | Date | Tue, 16 Nov 2021 00:30:07 +0100 |
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On 11/15/21 5:44 AM, Kajol Jain wrote: > Branch data available to bpf programs can be very useful to get > stack traces out of userspace applications. > > Commit fff7b64355ea ("bpf: Add bpf_read_branch_records() helper") > added bpf support to capture branch records in x86. Enable this feature > for powerpc as well. > > Commit 67306f84ca78 ("selftests/bpf: Add bpf_read_branch_records() > selftest") adds selftest corresponding to bpf branch read > function bpf_read_branch_records(). Used this selftest to > test bpf support, for reading branch records in powerpc. > > Selftest result in power9 box before this patch changes: > > [command]# ./test_progs -t perf_branches > Failed to load bpf_testmod.ko into the kernel: -8 > WARNING! Selftests relying on bpf_testmod.ko will be skipped. > test_perf_branches_common:PASS:test_perf_branches_load 0 nsec > test_perf_branches_common:PASS:attach_perf_event 0 nsec > test_perf_branches_common:PASS:set_affinity 0 nsec > check_good_sample:PASS:output not valid 0 nsec > check_good_sample:FAIL:read_branches_size err -2 > check_good_sample:FAIL:read_branches_stack err -2 > check_good_sample:FAIL:read_branches_stack stack bytes written=-2 > not multiple of struct size=24 > check_good_sample:FAIL:read_branches_global err -2 > check_good_sample:FAIL:read_branches_global global bytes written=-2 > not multiple of struct size=24 > check_good_sample:PASS:read_branches_size 0 nsec > #75/1 perf_branches_hw:FAIL > #75/2 perf_branches_no_hw:OK > #75 perf_branches:FAIL > Summary: 0/1 PASSED, 0 SKIPPED, 2 FAILED > > Selftest result in power9 box after this patch changes: > > [command]#: ./test_progs -t perf_branches > #75/1 perf_branches_hw:OK > #75/2 perf_branches_no_hw:OK > #75 perf_branches:OK > Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED > > Signed-off-by: Kajol Jain<kjain@linux.ibm.com> > --- > kernel/trace/bpf_trace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index fdd14072fc3b..2b7343b64bb7 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -1245,7 +1245,7 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto = { > BPF_CALL_4(bpf_read_branch_records, struct bpf_perf_event_data_kern *, ctx, > void *, buf, u32, size, u64, flags) > { > -#ifndef CONFIG_X86 > +#if !(defined(CONFIG_X86) || defined(CONFIG_PPC64))
Can this really be enabled generically? Looking at 3925f46bb590 ("powerpc/perf: Enable branch stack sampling framework") it says POWER8 [and beyond]. Should there be a generic Kconfig symbol like ARCH_HAS_BRANCH_RECORDS that can be selected by archs instead?
> return -ENOENT; > #else > static const u32 br_entry_size = sizeof(struct perf_branch_entry); >
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