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

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Date:   Thu, 6 Jun 2019 17:08:26 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     kan.liang@...ux.intel.com
Cc:     jolsa@...nel.org, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        ak@...ux.intel.com
Subject: Re: [PATCH V3 2/5] perf header: Add die information in CPU topology

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@...ux.intel.com escreveu:
> > From: Kan Liang <kan.liang@...ux.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@...hat.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@...el.com>
    Cc: Andi Kleen <ak@...ux.intel.com>
    Cc: Jiri Olsa <jolsa@...nel.org>
    Cc: Kan Liang <kan.liang@...ux.intel.com>
    Cc: Namhyung Kim <namhyung@...nel.org>
    Cc: Peter Zijlstra <peterz@...radead.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@...hat.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 */
 };
 
 Example: