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

[Ian Rogers <irogers@google.com>]

On Tue, Apr 9, 2024 at 8:34 AM Arnaldo Carvalho de Melo <acme@kernel.org> 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@redhat.com>
> > 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)?

Thanks,
Ian