[PATCH] perf test bpf: Skip test if kernel-debuginfo is not present
Athira Rajeev
atrajeev at linux.vnet.ibm.com
Tue Jan 3 00:42:50 AEDT 2023
> On 14-Dec-2022, at 9:21 PM, Arnaldo Carvalho de Melo <acme at kernel.org <mailto:acme at kernel.org>> wrote:
>
> Em Tue, Dec 13, 2022 at 03:21:03PM +0530, Athira Rajeev escreveu:
>>> On 13-Dec-2022, at 12:27 AM, Arnaldo Carvalho de Melo <acme at kernel.org <mailto:acme at kernel.org>> wrote:
>>> Em Thu, Nov 03, 2022 at 12:27:01PM +0530, Athira Rajeev escreveu:
>>>>> On 28-Oct-2022, at 9:12 PM, Kajol Jain <kjain at linux.ibm.com <mailto:kjain at linux.ibm.com>> wrote:
>>>>>
>>>>> Perf BPF filter test fails in environment where "kernel-debuginfo"
>>>>> is not installed.
>>>>>
>>>>> Test failure logs:
>>>>> <<>>
>>>>> 42: BPF filter :
>>>>> 42.1: Basic BPF filtering : Ok
>>>>> 42.2: BPF pinning : Ok
>>>>> 42.3: BPF prologue generation : FAILED!
>>>>> <<>>
>>>>>
>>>>> Enabling verbose option provided debug logs, which says debuginfo
>>>>> needs to be installed. Snippet of verbose logs:
>>>>>
>>>>> <<>>
>>>>> 42.3: BPF prologue generation :
>>>>> --- start ---
>>>>> test child forked, pid 28218
>>>>> <<>>
>>>>> Rebuild with CONFIG_DEBUG_INFO=y, or install an appropriate debuginfo
>>>>> package.
>>>>> bpf_probe: failed to convert perf probe events
>>>>> Failed to add events selected by BPF
>>>>> test child finished with -1
>>>>> ---- end ----
>>>>> BPF filter subtest 3: FAILED!
>>>>> <<>>
>>>>>
>>>>> Here subtest, "BPF prologue generation" failed and
>>>>> logs shows debuginfo is needed. After installing
>>>>> kernel-debuginfo package, testcase passes.
>>>>>
>>>>> Subtest "BPF prologue generation" failed because, the "do_test"
>>>>> function returns "TEST_FAIL" without checking the error type
>>>>> returned by "parse_events_load_bpf_obj" function.
>>>>> Function parse_events_load_bpf_obj can also return error of type
>>>>> "-ENOENT" incase kernel-debuginfo package is not installed. Fix this
>>>>> by adding check for -ENOENT error.
>>>>>
>>>>> Test result after the patch changes:
>>>>>
>>>>> Test failure logs:
>>>>> <<>>
>>>>> 42: BPF filter :
>>>>> 42.1: Basic BPF filtering : Ok
>>>>> 42.2: BPF pinning : Ok
>>>>> 42.3: BPF prologue generation : Skip (clang/debuginfo isn't
>>>>> installed or environment missing BPF support)
>>>>>
>>>>> Fixes: ba1fae431e74bb42 ("perf test: Add 'perf test BPF'")
>>>>> Signed-off-by: Kajol Jain <kjain at linux.ibm.com <mailto:kjain at linux.ibm.com>>
>>>>> Reviewed-by: Madhavan Srinivasan <maddy at linux.ibm.com <mailto:maddy at linux.ibm.com>>
>>>>> ---
>>>>> tools/perf/tests/bpf.c | 6 +++++-
>>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/tools/perf/tests/bpf.c b/tools/perf/tests/bpf.c
>>>>> index 17c023823713..57cecadc1da2 100644
>>>>> --- a/tools/perf/tests/bpf.c
>>>>> +++ b/tools/perf/tests/bpf.c
>>>>> @@ -126,6 +126,10 @@ static int do_test(struct bpf_object *obj, int (*func)(void),
>>>>>
>>>>> err = parse_events_load_bpf_obj(&parse_state, &parse_state.list, obj, NULL);
>>>>> parse_events_error__exit(&parse_error);
>>>>> + if (err == -ENOENT) {
>>>>> + pr_debug("Failed to add events selected by BPF, debuginfo package not installed\n");
>>>>> + return TEST_SKIP;
>>>>> + }
>>>>
>>>> Hi Kajol,
>>>>
>>>> Here, you have used ENOENT to skip the test. But there could be other places in the code path for “parse_events_load_bpf_obj”
>>>> which also returns ENOENT. In that case, for any exit that returns ENOENT, test will get skipped.
>>>>
>>>> Can we look at the logs, example we have this in commit logs:
>>>>
>>>> Rebuild with CONFIG_DEBUG_INFO=y, or install an appropriate debuginfo
>>>> package.
>>>>
>>>> so as to decide whether to skip for debug info ?
>>>
>>> Kajol?
>
>> Hi Arnaldo, looking for your suggestion on how to handle the case where debuginfo is missing.
>
>> Here the bpf test fails because of missing debuginfo. The function
>> which goes through the debuginfo check is "parse_events_load_bpf_obj"
>> . parse_events_load_bpf_obj internally calls "open_debuginfo" which
>> returns ENOENT when debuginfo is missing. The patch fix from Kajol is
>> to skip the test using error code ENOENT for debuginfo.
>
> Lets see:
>
> root at roc-rk3399-pc:~# uname -a
> Linux roc-rk3399-pc 6.1.0-rc5-00123-g4dd7ff4a0311 #2 SMP PREEMPT Wed Nov 16 19:55:11 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux
> root at roc-rk3399-pc:~# perf probe -x ~/bin/perf open_debuginfo
> Added new event:
> probe_perf:open_debuginfo (on open_debuginfo in /home/acme/bin/perf)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe_perf:open_debuginfo -aR sleep 1
>
> root at roc-rk3399-pc:~#
>
> root at roc-rk3399-pc:~# perf trace --call-graph=dwarf -a -e probe_perf:* perf test bpf
> 40: LLVM search and compile :
> 40.1: Basic BPF llvm compile : Ok
> 40.3: Compile source for BPF prologue generation : FAILED!
> 40.4: Compile source for BPF relocation : Ok
> 42: BPF filter :
> 42.1: Basic BPF filtering : 0.000 perf/38363 probe_perf:open_debuginfo(__probe_ip: 187650778659428)
> open_debuginfo (/home/acme/bin/perf)
> try_to_find_probe_trace_events (inlined)
> convert_to_probe_trace_events (inlined)
> convert_perf_probe_events (/home/acme/bin/perf)
> bpf__probe (/home/acme/bin/perf)
> parse_events_load_bpf_obj (/home/acme/bin/perf)
> do_test (/home/acme/bin/perf)
> FAILED!
> 42.2: BPF pinning : 5594.218 perf/38582 probe_perf:open_debuginfo(__probe_ip: 187650778659428)
> open_debuginfo (/home/acme/bin/perf)
> try_to_find_probe_trace_events (inlined)
> convert_to_probe_trace_events (inlined)
> convert_perf_probe_events (/home/acme/bin/perf)
> bpf__probe (/home/acme/bin/perf)
> parse_events_load_bpf_obj (/home/acme/bin/perf)
> do_test (/home/acme/bin/perf)
> FAILED!
> 42.3: BPF prologue generation : FAILED!
> 63: Test libpfm4 support :
> 99: perf stat --bpf-counters test : Skip
> 100: perf stat --bpf-counters --for-each-cgroup test : Skip
> root at roc-rk3399-pc:~#
>
> So that is the callchains leading to open_debuginfo(), perhaps we should
> return ENODATA at try_to_find_probe_trace_events() when open_debuginfo()
> fails?
Hi Arnaldo,
Thanks for the suggestions. I tried with changing return code to ENODATA when open_debuginfo fails and will
send a separate patch addressing this change.
>
> ⬢[acme at toolbox perf]$ find tools/perf/ -name "*.[ch]" | xargs grep try_to_find_probe_trace_events
> tools/perf/util/probe-event.c:static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
> tools/perf/util/probe-event.c:static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
> tools/perf/util/probe-event.c: ret = try_to_find_probe_trace_events(pev, tevs);
> ⬢[acme at toolbox perf]$
>
> Also it returns ENOENT as well when not finding the probe point... There
> we should return perhaps ENOSYM?
ENOSYM is not defined for all the archs.
arch/parisc/include/uapi/asm/errno.h:#define ENOSYM 215 /* symbol does not exist in executable */
So we need to make this error code generic to use in probe-event. Shall we make this error code
generic for all archs to use ?
Thanks
Athira
>
>> But issue with using this return code is that, there are other places
>> in the code path for "parse_events_load_bpf_obj" which also returns
>> ENOENT. In that case, for any exit path that returns ENOENT, test will
>> get skipped. Hence looking for an alternative way to identify missing
>> debuginfo to skip the test. Please share your thoughts on this.
>
> See above.
>
> - Arnaldo
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