linux-kernel - [PATCH 5.4 057/165] perf header: Fix false warning when there are no duplicate cache entries

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Message-Id: <20200111094926.006892306@linuxfoundation.org>
Date:   Sat, 11 Jan 2020 10:49:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michael Petlan <mpetlan@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 057/165] perf header: Fix false warning when there are no duplicate cache entries

From: Michael Petlan <mpetlan@...hat.com>

[ Upstream commit 28707826877f84bce0977845ea529cbdd08e4e8d ]

Before this patch, perf expected that there might be NPROC*4 unique
cache entries at max, however, it also expected that some of them would
be shared and/or of the same size, thus the final number of entries
would be reduced to be lower than NPROC*4. In case the number of entries
hadn't been reduced (was NPROC*4), the warning was printed.

However, some systems might have unusual cache topology, such as the
following two-processor KVM guest:

	cpu  level  shared_cpu_list  size
	  0     1         0           32K
	  0     1         0           64K
	  0     2         0           512K
	  0     3         0           8192K
	  1     1         1           32K
	  1     1         1           64K
	  1     2         1           512K
	  1     3         1           8192K

This KVM guest has 8 (NPROC*4) unique cache entries, which used to make
perf printing the message, although there actually aren't "way too many
cpu caches".

v2: Removing unused argument.

v3: Unifying the way we obtain number of cpus.

v4: Removed '& UINT_MAX' construct which is redundant.

Signed-off-by: Michael Petlan <mpetlan@...hat.com>
Acked-by: Jiri Olsa <jolsa@...hat.com>
LPU-Reference: 20191208162056.20772-1-mpetlan@...hat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/perf/util/header.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index becc2d109423..d3412f2c0d18 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1089,21 +1089,18 @@ static void cpu_cache_level__fprintf(FILE *out, struct cpu_cache_level *c)
 	fprintf(out, "L%d %-15s %8s [%s]\n", c->level, c->type, c->size, c->map);
 }
 
-static int build_caches(struct cpu_cache_level caches[], u32 size, u32 *cntp)
+#define MAX_CACHE_LVL 4
+
+static int build_caches(struct cpu_cache_level caches[], u32 *cntp)
 {
 	u32 i, cnt = 0;
-	long ncpus;
 	u32 nr, cpu;
 	u16 level;
 
-	ncpus = sysconf(_SC_NPROCESSORS_CONF);
-	if (ncpus < 0)
-		return -1;
-
-	nr = (u32)(ncpus & UINT_MAX);
+	nr = cpu__max_cpu();
 
 	for (cpu = 0; cpu < nr; cpu++) {
-		for (level = 0; level < 10; level++) {
+		for (level = 0; level < MAX_CACHE_LVL; level++) {
 			struct cpu_cache_level c;
 			int err;
 
@@ -1123,18 +1120,12 @@ static int build_caches(struct cpu_cache_level caches[], u32 size, u32 *cntp)
 				caches[cnt++] = c;
 			else
 				cpu_cache_level__free(&c);
-
-			if (WARN_ONCE(cnt == size, "way too many cpu caches.."))
-				goto out;
 		}
 	}
- out:
 	*cntp = cnt;
 	return 0;
 }
 
-#define MAX_CACHE_LVL 4
-
 static int write_cache(struct feat_fd *ff,
 		       struct evlist *evlist __maybe_unused)
 {
@@ -1143,7 +1134,7 @@ static int write_cache(struct feat_fd *ff,
 	u32 cnt = 0, i, version = 1;
 	int ret;
 
-	ret = build_caches(caches, max_caches, &cnt);
+	ret = build_caches(caches, &cnt);
 	if (ret)
 		goto out;
 
-- 
2.20.1