Re: BISECTED: perf test 'Miscellaneous Intel PT' failing on Intel hybrid machines

[Adrian Hunter]

On 9/04/24 22:05, Adrian Hunter wrote:
> On 9/04/24 18:46, Ian Rogers wrote:
>> On Tue, Apr 9, 2024 at 8:34 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>>>
>>> On Tue, Apr 09, 2024 at 12:32:06PM -0300, Arnaldo Carvalho de Melo wrote:
>>>> root@x1:~# perf test "Miscellaneous Intel PT testing"
>>>> 112: Miscellaneous Intel PT testing                                  : FAILED!
>>>> root@x1:~#
>>>>
>>>> then I revert:
>>>>
>>>> commit 642e1ac96aaa12aeb41402e68eac7faf5917a67a (HEAD -> perf-tools-next)
>>>> Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
>>>> Date:   Tue Apr 9 12:28:49 2024 -0300
>>>>
>>>>     Revert "perf pmus: Check if we can encode the PMU number in perf_event_attr.type"
>>>>
>>>>     This reverts commit 82fe2e45cdb00de4fa648050ae33bdadf9b3294a.
>>>> ⬢[acme@toolbox perf-tools-next]$
>>>>
>>>> It works now:
>>>>
>>>> root@x1:~# perf -v
>>>> perf version 6.8.g642e1ac96aaa
>>>> root@x1:~# perf test "Miscellaneous Intel PT testing"
>>>> 117: Miscellaneous Intel PT testing                                  : Ok
>>>> root@x1:~#
>>>>
>>>> Investigating, if you come up with ideas, lemme know.
>>>
>>> Some more context:
>>>
>>> When this patch was implemented/tested I had access only to an ARM64
>>> hybrid machine, now my notebook is a Rocket Lake lenovo (13th gen), that
>>> is hybrid and the test is failing with:
>>>
>>> root@x1:~# perf test -v "Miscellaneous Intel PT testing"
>>> 112: Miscellaneous Intel PT testing                                  :
>>> --- start ---
>>> test child forked, pid 304355
>>> --- Test system-wide sideband ---
>>> Checking for CPU-wide recording on CPU 0
>>> OK
>>> Checking for CPU-wide recording on CPU 1
>>> OK
>>> Linux
>>> [ perf record: Woken up 1 times to write data ]
>>> [ perf record: Captured and wrote 1.934 MB /tmp/perf-test-intel-pt-sh.xACV6V7Hn4/test-perf.data ]
>>> OK
>>> --- Test per-thread recording ---
>>> Workload PIDs are 304377 and 304378
>>> perf PID is 304389
>>> Waiting for "perf record has started" message
>>> OK
>>> pid 0 cpu -1 fd 5 : sys_perf_event_open: pid 0  cpu -1  group_fd -1  flags 0x8 = 5
>>> pid 0 cpu -1 fd 6 : sys_perf_event_open: pid 0  cpu -1  group_fd -1  flags 0x8 = 6
>>> pid 304377 cpu -1 fd 7 : sys_perf_event_open: pid 304377  cpu -1  group_fd -1  flags 0x8 = 7
>>> pid 304380 cpu -1 fd 8 : sys_perf_event_open: pid 304380  cpu -1  group_fd -1  flags 0x8 = 8
>>> pid 304378 cpu -1 fd 9 : sys_perf_event_open: pid 304378  cpu -1  group_fd -1  flags 0x8 = 9
>>> pid 304381 cpu -1 fd 10 : sys_perf_event_open: pid 304381  cpu -1  group_fd -1  flags 0x8 = 10
>>> pid 304377 cpu -1 fd 11 : sys_perf_event_open: pid 304377  cpu -1  group_fd -1  flags 0x8 = 11
>>> pid 304380 cpu -1 fd 12 : sys_perf_event_open: pid 304380  cpu -1  group_fd -1  flags 0x8 = 12
>>> pid 304378 cpu -1 fd 13 : sys_perf_event_open: pid 304378  cpu -1  group_fd -1  flags 0x8 = 13
>>> pid 304381 cpu -1 fd 14 : sys_perf_event_open: pid 304381  cpu -1  group_fd -1  flags 0x8 = 14
>>> fd 7 : idx 0: mmapping fd 7
>>> fd 11 fd_to 7 : idx 0: set output fd 11 -> 7
>>> fd 8 : idx 1: mmapping fd 8
>>> fd 12 fd_to 8 : idx 1: set output fd 12 -> 8
>>> fd 9 : idx 2: mmapping fd 9
>>> fd 13 fd_to 9 : idx 2: set output fd 13 -> 9
>>> fd 10 : idx 3: mmapping fd 10
>>> fd 14 fd_to 10 : idx 3: set output fd 14 -> 10
>>> Checking 10 fds
>>> No mmap for fd 5
>>
>> Thanks Arnaldo, so the reverted change is:
>> ```
>> --- a/tools/perf/util/pmus.c
>> +++ b/tools/perf/util/pmus.c
>> @@ -4,6 +4,7 @@
>> #include <subcmd/pager.h>
>> #include <sys/types.h>
>> #include <dirent.h>
>> +#include <pthread.h>
>> #include <string.h>
>> #include <unistd.h>
>> #include "debug.h"
>> @@ -492,9 +493,35 @@ int perf_pmus__num_core_pmus(void)
>>        return count;
>> }
>>
>> +static bool __perf_pmus__supports_extended_type(void)
>> +{
>> +       struct perf_pmu *pmu = NULL;
>> +
>> +       if (perf_pmus__num_core_pmus() <= 1)
>> +               return false;
>> +
>> +       while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
>> +               if (!is_event_supported(PERF_TYPE_HARDWARE,
>> PERF_COUNT_HW_CPU_CYCLES | ((__u64)pmu->
>> type << PERF_PMU_TYPE_SHIFT)))
>> +                       return false;
>> +       }
>> +
>> +       return true;
>> +}
>> +
>> +static bool perf_pmus__do_support_extended_type;
>> +
>> +static void perf_pmus__init_supports_extended_type(void)
>> +{
>> +       perf_pmus__do_support_extended_type =
>> __perf_pmus__supports_extended_type();
>> +}
>> +
>> bool perf_pmus__supports_extended_type(void)
>> {
>> -       return perf_pmus__num_core_pmus() > 1;
>> +       static pthread_once_t extended_type_once = PTHREAD_ONCE_INIT;
>> +
>> +       pthread_once(&extended_type_once,
>> perf_pmus__init_supports_extended_type);
>> +
>> +       return perf_pmus__do_support_extended_type;
>> }
>>
>> struct perf_pmu *evsel__find_pmu(const struct evsel *evsel)
>> ```
>> On your Intel this should have previously returned true as
>> "perf_pmus__num_core_pmus() > 1", and with the new code presumably
>> is_event_supported is returning false. Could you dump the PMU's name
>> at that point? Is cpu_core or cpu_atom looking like it doesn't support
>> the event? Is the test failing when run as root (ie is
>> is_event_supported failing to have expected fallback paths)?
> 
> Problem is the test scrapes debug output and is_event_supported()
> prints out debug that confuses the test.  Other probe functions
> like in perf_api_probe.c use sys_perf_event_open() so the issue
> has not arisen before.

Patch here:

	https://lore.kernel.org/all/20240410104450.15602-1-adrian.hunter@xxxxxxxxx/