linux-kernel - [PATCH v3 1/7] perf: Increase the maximum number of branches remove

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250523-b4-ctr_upstream_v3-v3-1-ad355304ba1c@rivosinc.com>
Date: Fri, 23 May 2025 00:25:07 +0100
From: Rajnesh Kanwal <rkanwal@...osinc.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Arnaldo Carvalho de Melo <acme@...nel.org>, 
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
 Adrian Hunter <adrian.hunter@...el.com>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Atish Kumar Patra <atishp@...osinc.com>, 
 Anup Patel <anup@...infault.org>, Will Deacon <will@...nel.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Beeman Strong <beeman@...osinc.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
 Palmer Dabbelt <palmer@...ive.com>, Conor Dooley <conor@...nel.org>, 
 devicetree@...r.kernel.org, Rajnesh Kanwal <rkanwal@...osinc.com>
Subject: [PATCH v3 1/7] perf: Increase the maximum number of branches
 remove_loops() can process.

RISCV CTR extension supports a maximum depth of 256 last branch records.
Currently remove_loops() can only process 127 entries at max. This leads
to samples with more than 127 entries being skipped. This change simply
updates the remove_loops() logic to be able to process 256 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 2d51badfbf2e2d1588fa4fdd42ef6c8fea35bf0e..5414528b9d336790decfb42a4f6a4da6c6b68b07 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2176,25 +2176,32 @@ 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) {

-- 
2.43.0