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Subject[PATCH AUTOSEL 5.4 075/187] perf header: Fix false warning when there are no duplicate cache entries
Date
From: Michael Petlan <mpetlan@redhat.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@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
LPU-Reference: 20191208162056.20772-1-mpetlan@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.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
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