Re: [PATCH V3 2/5] perf header: Add die information in CPU topology

Arnaldo Carvalho de Melo
2019-06-06T20:08:34Z

Em Thu, Jun 06, 2019 at 04:12:10PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jun 04, 2019 at 03:50:41PM -0700, kan.liang@linux.intel.com escreveu:
> > From: Kan Liang <kan.liang@linux.intel.com>
> >
> > With the new CPUID.1F, a new level type of CPU topology, 'die', is
> > introduced. The 'die' information in CPU topology should be added in
> > perf header.
> >
> > To be compatible with old perf.data, the patch checks the section size
> > before reading the die information. The new info is added at the end of
> > the cpu_topology section, the old perf tool ignores the extra data.
> > It never reads data crossing the section boundary.
> >
> > The new perf tool with the patch can be used on legacy kernel. Add a
> > new function has_die_topology() to check if die topology information is
> > supported by kernel. The function only check X86 and CPU 0. Assuming
> > other CPUs have same topology.
>
> You're changing the header, how would a new tool handle an old perf.data
> where this 'die_id' is not present? What about an old tool dealing with
> a perf.data with this die_id?
>
> I couldn't see any provision for that, am I missing something?
>
> /me goes to read tools/perf/util/cputopo.c ...
>
> Yeah, its just the description on the perf.data doc file that confused
> me, I'll clarify that after finishing reviewing/applying this patchkit.

So I have this on top, please check.

- Arnaldo

commit a9396a70fc7101c108e1c91fa1771557bbbb57a1
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date: Thu Jun 6 17:03:18 2019 -0300

perf data: Fix perf.data documentation for HEADER_CPU_TOPOLOGY

The 'die' info isn't in the same array as core and socket ids, and we
missed the 'dies' string list, that comes right after the 'core' +
'socket' id variable length array, followed by the VLA for the dies.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: c9cb12c5ba08 ("perf header: Add die information in CPU topology")
Link: https://lkml.kernel.org/n/tip-nubi6mxp2n8ofvlx7ph6k3h6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
index de78183f6881..5f54feb19977 100644
--- a/tools/perf/Documentation/perf.data-file-format.txt
+++ b/tools/perf/Documentation/perf.data-file-format.txt
@@ -151,20 +151,35 @@ struct {

HEADER_CPU_TOPOLOGY = 13,

-String lists defining the core and CPU threads topology.
-The string lists are followed by a variable length array
-which contains core_id, die_id (for x86) and socket_id of each cpu.
-The number of entries can be determined by the size of the
-section minus the sizes of both string lists.
-
struct {
+ /*
+ * First revision of HEADER_CPU_TOPOLOGY
+ *
+ * See 'struct perf_header_string_list' definition earlier
+ * in this file.
+ */
+
struct perf_header_string_list cores; /* Variable length */
struct perf_header_string_list threads; /* Variable length */
+
+ /*
+ * Second revision of HEADER_CPU_TOPOLOGY, older tools
+ * will not consider what comes next
+ */
+
struct {
uint32_t core_id;
- uint32_t die_id;
uint32_t socket_id;
} cpus[nr]; /* Variable length records */
+ /* 'nr' comes from previously processed HEADER_NRCPUS's nr_cpu_avail */
+
+ /*
+ * Third revision of HEADER_CPU_TOPOLOGY, older tools
+ * will not consider what comes next
+ */
+
+ struct perf_header_string_list dies; /* Variable length */
+ uint32_t die_id[nr_cpus_avail]; /* from previously processed HEADER_NR_CPUS, VLA */
};