| Message ID | 20211115044437.12047-1-kjain@linux.ibm.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: Enable bpf support for reading branch records in powerpc | expand |
| Context | Check | Description |
|---|---|---|
| bpf/vmtest-bpf-PR | fail | PR summary |
| bpf/vmtest-bpf-next-PR | fail | PR summary |
| bpf/vmtest-bpf | fail | VM_Test |
| bpf/vmtest-bpf-next | fail | VM_Test |
| netdev/tree_selection | success | Guessing tree name failed - patch did not apply |
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); >
On Tue, Nov 16, 2021 at 12:30:07AM +0100, Daniel Borkmann wrote: > > 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? I conplained about it before as well. I'd just take it out entirely. If perf_snapshot_branch_stack isn't implemnted it'll return 0 and then we'll -Esomething anyway.
On 11/16/21 2:04 PM, Peter Zijlstra wrote: > On Tue, Nov 16, 2021 at 12:30:07AM +0100, Daniel Borkmann wrote: > >>> 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? > Hi Peterz/Daniel, Thanks for reviewing the patch > I conplained about it before as well. I'd just take it out entirely. I agree, it make more sense to entirely remove this arch check from here. Because anyway, incase any arch doesn't support this functionality, bpf_read_branch_records will return -EINVAL. > > If perf_snapshot_branch_stack isn't implemnted it'll return 0 and then > we'll -Esomething anyway. In this patch, we are basically adding powerpc support to capture branch records via bpf_read_branch_records function. We are still looking into adding support for perf_snapshot_branch_stack for powerpc. I will send a follow up to remove arch check in bpf_read_branch_records function. Thanks, Kajol Jain > >
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)) return -ENOENT; #else static const u32 br_entry_size = sizeof(struct perf_branch_entry);
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(-)