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Message-Id: <20240529185337.182722-2-rkanwal@rivosinc.com>
Date: Wed, 29 May 2024 19:53:32 +0100
From: Rajnesh Kanwal <rkanwal@...osinc.com>
To: linux-kernel@...r.kernel.org
Cc: linux-perf-users@...r.kernel.org,
linux-riscv@...ts.infradead.org,
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Rajnesh Kanwal <rkanwal@...osinc.com>
Subject: [PATCH RFC 1/6] perf: Increase the maximum number of samples to 256.
RISCV CTR extension support a maximum depth of 256 last branch records.
The 127 entries limit results in corrupting CTR entries for RISC-V if
configured to be 256 entries. This will not impact any other architectures
as it is just increasing maximum limit of possible entries.
Signed-off-by: Rajnesh Kanwal <rkanwal@...osinc.com>
---
tools/perf/util/machine.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 527517db3182..ec12f0199d46 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2254,25 +2254,32 @@ static void save_iterations(struct iterations *iter,
iter->cycles += be[i].flags.cycles;
}
-#define CHASHSZ 127
-#define CHASHBITS 7
-#define NO_ENTRY 0xff
+#define CHASHBITS 8
+#define NO_ENTRY 0xffU
-#define PERF_MAX_BRANCH_DEPTH 127
+#define PERF_MAX_BRANCH_DEPTH 256
/* Remove loops. */
+/* Note: Last entry (i==ff) will never be checked against NO_ENTRY
+ * so it's safe to have an unsigned char array to process 256 entries
+ * without causing clash between last entry and NO_ENTRY value.
+ */
static int remove_loops(struct branch_entry *l, int nr,
struct iterations *iter)
{
int i, j, off;
- unsigned char chash[CHASHSZ];
+ unsigned char chash[PERF_MAX_BRANCH_DEPTH];
memset(chash, NO_ENTRY, sizeof(chash));
- BUG_ON(PERF_MAX_BRANCH_DEPTH > 255);
+ BUG_ON(PERF_MAX_BRANCH_DEPTH > 256);
for (i = 0; i < nr; i++) {
- int h = hash_64(l[i].from, CHASHBITS) % CHASHSZ;
+ /* Remainder division by PERF_MAX_BRANCH_DEPTH is not
+ * needed as hash_64 will anyway limit the hash
+ * to CHASHBITS
+ */
+ int h = hash_64(l[i].from, CHASHBITS);
/* no collision handling for now */
if (chash[h] == NO_ENTRY) {
--
2.34.1
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