[PATCH v2 0/2] perf alpha: Decode ProfileMe samples

[PATCH v2 0/2] perf alpha: Decode ProfileMe samples

[Matt Turner]

The Alpha kernel series "alpha/perf: add ProfileMe sampling" adds
ProfileMe sampling to the Alpha cpu PMU. Each ProfileMe sample carries
the profiled instruction's PMPC and its I_STAT and PCTR_CTL status as
PERF_SAMPLE_RAW data, which says whether the instruction retired,
whether it trapped and why, whether it was a mispredicted branch,
stalled before map, or was killed on a wrong path, and what PCTR1
counted while it was in flight:

  https://lore.kernel.org/r/20261030-alpha-profileme-v2-0-c702f1c65272@gmail.com

This series is the perf tool side. Patch 1 decodes the raw data in perf
report -D and perf script -D, as is done for AMD IBS. It copies the new
uapi header from the kernel series into tools/arch, so it should wait
until that header is merged. Patch 2 adds a script that sums the status
by symbol or by instruction, in the style of DCPI.

To try it, with the kernel series applied:

  perf record -R -e instructions:p -- ./workload
  tools/perf/python/alpha-profileme.py --pc

I tested this on an AlphaServer ES47 (EV7). Sampling a loop whose
branch tests random data reports that branch mispredicted in 21% of its
samples, and 0% with sorted data.

Signed-off-by: Matt Turner <mattst88@gmail.com>
---
Changes in v2:
- Patch 1: copy the raw data out of the sample and convert it from
  little endian, so that it decodes on strict-alignment and big-endian
  hosts.
- Patches 1 and 2: follow the new 28-byte struct alpha_profileme_sample
  from kernel v2.
- Link to v1: https://patch.msgid.link/20261028-perf-alpha-profileme-v1-0-f46c1938d001@gmail.com

To: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@redhat.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Namhyung Kim <namhyung@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Jiri Olsa <jolsa@kernel.org>
To: Ian Rogers <irogers@google.com>
To: Adrian Hunter <adrian.hunter@intel.com>
To: James Clark <james.clark@linaro.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-perf-users@vger.kernel.org

---
Matt Turner (2):
      perf alpha: Decode ProfileMe raw samples
      perf python: Add alpha-profileme.py

 tools/arch/alpha/include/uapi/asm/perf_event.h |  31 +++++
 tools/perf/check-headers.sh                    |   1 +
 tools/perf/python/alpha-profileme.py           | 162 +++++++++++++++++++++++++
 tools/perf/util/Build                          |   1 +
 tools/perf/util/alpha-sample-raw.c             | 145 ++++++++++++++++++++++
 tools/perf/util/sample-raw.c                   |   2 +
 tools/perf/util/sample-raw.h                   |   2 +
 7 files changed, 344 insertions(+)
---
base-commit: 4626d370ae89b8af4d46a45372b269f926ec662d
change-id: 20261028-perf-alpha-profileme-8010299be323

Best regards,
--  
Matt Turner <mattst88@gmail.com>

[PATCH v2 1/2] perf alpha: Decode ProfileMe raw samples

[Matt Turner]

The Alpha cpu PMU attaches struct alpha_profileme_sample to each
ProfileMe sample as PERF_SAMPLE_RAW data: the profiled instruction's
PMPC along with the I_STAT and PCTR_CTL status that says what happened
to it.

Decode it in perf report -D and perf script -D the way AMD IBS raw data
is decoded, naming the trap from TRAP_TYPE when TRP is set and from the
PALcode entry offset in PMPC for redirect traps, which TRAP_TYPE does
not report. The payload is copied out of the sample and converted from
little endian, so that it decodes on strict-alignment and big-endian
hosts too.

Copy the uapi header that defines the struct into tools/arch and add it
to check-headers.sh.

Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 tools/arch/alpha/include/uapi/asm/perf_event.h |  31 ++++++
 tools/perf/check-headers.sh                    |   1 +
 tools/perf/util/Build                          |   1 +
 tools/perf/util/alpha-sample-raw.c             | 145 +++++++++++++++++++++++++
 tools/perf/util/sample-raw.c                   |   2 +
 tools/perf/util/sample-raw.h                   |   2 +
 6 files changed, 182 insertions(+)

diff --git a/tools/arch/alpha/include/uapi/asm/perf_event.h b/tools/arch/alpha/include/uapi/asm/perf_event.h
new file mode 100644
index 000000000000..aa0eff5a917c
--- /dev/null
+++ b/tools/arch/alpha/include/uapi/asm/perf_event.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_ASM_ALPHA_PERF_EVENT_H
+#define _UAPI_ASM_ALPHA_PERF_EVENT_H
+
+#include <linux/types.h>
+
+/*
+ * PERF_SAMPLE_RAW payload of a ProfileMe sample from the cpu PMU.
+ *
+ * pmpc, i_stat and pctr_ctl are the values of the PMPC, I_STAT and
+ * PCTR_CTL registers when the ProfileMe window closed. i_stat holds only
+ * bits 40:30 and pctr_ctl only bits 47:0. See the EV67/EV68 Hardware
+ * Reference Manuals for the field layout.
+ *
+ * In the sample record the payload follows the 32-bit PERF_SAMPLE_RAW
+ * size, so it starts 4 bytes past an 8-byte boundary. The 64-bit fields
+ * are packed after the 32-bit version so that they are 8-byte aligned in
+ * the record and no padding follows the payload.
+ *
+ * Fields may be added to the end in later versions.
+ */
+#define ALPHA_PROFILEME_SAMPLE_VERSION	1
+
+struct alpha_profileme_sample {
+	__u32 version;
+	__u64 pmpc __attribute__((packed));
+	__u64 i_stat __attribute__((packed));
+	__u64 pctr_ctl __attribute__((packed));
+};
+
+#endif /* _UAPI_ASM_ALPHA_PERF_EVENT_H */
diff --git a/tools/perf/check-headers.sh b/tools/perf/check-headers.sh
index 531c0e0e84df..de66bb148754 100755
--- a/tools/perf/check-headers.sh
+++ b/tools/perf/check-headers.sh
@@ -36,6 +36,7 @@ declare -a FILES=(
   "arch/x86/include/asm/msr-index.h"
   "arch/x86/lib/x86-opcode-map.txt"
   "arch/x86/tools/gen-insn-attr-x86.awk"
+  "arch/alpha/include/uapi/asm/perf_event.h"
   "arch/arm/include/uapi/asm/perf_regs.h"
   "arch/arm64/include/uapi/asm/perf_regs.h"
   "arch/loongarch/include/uapi/asm/perf_regs.h"
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 2c1f880c4c47..2ab63bbe4a05 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -77,6 +77,7 @@ perf-util-y += sample.o
 perf-util-y += sample-raw.o
 perf-util-y += s390-sample-raw.o
 perf-util-y += amd-sample-raw.o
+perf-util-y += alpha-sample-raw.o
 perf-util-y += ordered-events.o
 perf-util-y += namespaces.o
 perf-util-y += comm.o
diff --git a/tools/perf/util/alpha-sample-raw.c b/tools/perf/util/alpha-sample-raw.c
new file mode 100644
index 000000000000..b4e336d8fc8f
--- /dev/null
+++ b/tools/perf/util/alpha-sample-raw.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Alpha specific. Provide textual annotation for ProfileMe raw sample data.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <linux/kernel.h>
+#include <linux/perf_event.h>
+
+#include "../../arch/alpha/include/uapi/asm/perf_event.h"
+
+#include "evlist.h"
+#include "evsel.h"
+#include "sample-raw.h"
+#include "util/sample.h"
+
+/* I_STAT */
+#define I_STAT_OVR(x)		(((x) >> 30) & 0x7)
+#define I_STAT_ICM(x)		(((x) >> 33) & 0x1)
+#define I_STAT_TRAP_TYPE(x)	(((x) >> 34) & 0xf)
+#define I_STAT_LSO(x)		(((x) >> 38) & 0x1)
+#define I_STAT_TRP(x)		(((x) >> 39) & 0x1)
+#define I_STAT_MIS(x)		(((x) >> 40) & 0x1)
+
+/* PCTR_CTL */
+#define PCTR_CTL_TAK(x)		((x) & 0x1)
+#define PCTR_CTL_VAL(x)		(((x) >> 1) & 0x1)
+#define PCTR_CTL_SL1(x)		(((x) >> 2) & 0x3)
+#define PCTR_CTL_SL0(x)		(((x) >> 4) & 0x1)
+#define PCTR_CTL_PCTR1(x)	(((x) >> 6) & 0xfffff)
+#define PCTR_CTL_KILLED(x)	(((x) >> 26) & 0x1)
+#define PCTR_CTL_STALLED(x)	(((x) >> 27) & 0x1)
+#define PCTR_CTL_PCTR0(x)	(((x) >> 28) & 0xfffff)
+
+/* PMPC */
+#define PMPC_PAL(x)		((x) & 0x1)
+#define PMPC_PAL_OFFSET(x)	((x) & 0x7fff)
+
+static const char * const trap_type_names[16] = {
+	[0]  = "replay",
+	[2]  = "DTB double miss (3 level)",
+	[3]  = "DTB double miss (4 level)",
+	[4]  = "FP disabled",
+	[5]  = "unaligned",
+	[6]  = "DTB single miss",
+	[7]  = "Dstream fault",
+	[8]  = "OPCDEC",
+	[10] = "machine check",
+	[12] = "arithmetic",
+	[14] = "MT_FPCR",
+	[15] = "reset",
+};
+
+/* What PCTR1 counts during the window, by SL1. */
+static const char * const pctr1_names[4] = {
+	"cycles",
+	"retire delay",
+	"bcache misses",
+	"mbox replays",
+};
+
+static const char *trap_name(__u64 i_stat, __u64 pmpc)
+{
+	const char *name;
+
+	/* Redirect traps leave TRAP_TYPE alone and are named by PMPC. */
+	if (PMPC_PAL(pmpc)) {
+		switch (PMPC_PAL_OFFSET(pmpc)) {
+		case 0x481:
+			return "Istream access violation";
+		case 0x581:
+			return "ITB miss";
+		case 0x681:
+			return "interrupt";
+		default:
+			break;
+		}
+	}
+	if (!I_STAT_TRP(i_stat) || I_STAT_MIS(i_stat))
+		return "none";
+	name = trap_type_names[I_STAT_TRAP_TYPE(i_stat)];
+	return name ? name : "other (see PMPC)";
+}
+
+/*
+ * Copy the payload out of the sample, since nothing guarantees its
+ * alignment in the buffer, and convert it from the little-endian byte
+ * order it was recorded in.
+ */
+static bool is_profileme_sample(struct evlist *evlist, union perf_event *event,
+				struct perf_sample *sample,
+				struct alpha_profileme_sample *pm)
+{
+	struct evsel *evsel;
+
+	if (sample->raw_size < sizeof(*pm))
+		return false;
+
+	evsel = evlist__event2evsel(evlist, event);
+	if (!evsel)
+		return false;
+	if (evsel->core.attr.type != PERF_TYPE_HARDWARE &&
+	    evsel->core.attr.type != PERF_TYPE_RAW)
+		return false;
+
+	memcpy(pm, sample->raw_data, sizeof(*pm));
+	pm->version = le32_to_cpu(pm->version);
+	pm->pmpc = le64_to_cpu(pm->pmpc);
+	pm->i_stat = le64_to_cpu(pm->i_stat);
+	pm->pctr_ctl = le64_to_cpu(pm->pctr_ctl);
+
+	return pm->version >= ALPHA_PROFILEME_SAMPLE_VERSION;
+}
+
+void evlist__alpha_sample_raw(struct evlist *evlist, union perf_event *event,
+			      struct perf_sample *sample)
+{
+	struct alpha_profileme_sample pm;
+	unsigned long long i_stat, ctl, pmpc;
+
+	if (event->header.type != PERF_RECORD_SAMPLE ||
+	    !is_profileme_sample(evlist, event, sample, &pm))
+		return;
+
+	i_stat = pm.i_stat;
+	ctl = pm.pctr_ctl;
+	pmpc = pm.pmpc;
+
+	printf("ProfileMe PMPC:\t%016llx %s trap %s%s\n",
+	       pmpc, PMPC_PAL(pmpc) ? "PAL" : (pmpc >> 63 ? "kernel" : "user"),
+	       trap_name(i_stat, pmpc),
+	       I_STAT_TRP(i_stat) && I_STAT_MIS(i_stat) ? " mispredicted" : "");
+	printf("ProfileMe I_STAT:\t%016llx TRP %d MIS %d LSO %d TrapType %d ICM %d OVR %d\n",
+	       i_stat, (int)I_STAT_TRP(i_stat), (int)I_STAT_MIS(i_stat),
+	       (int)I_STAT_LSO(i_stat), (int)I_STAT_TRAP_TYPE(i_stat),
+	       (int)I_STAT_ICM(i_stat), (int)I_STAT_OVR(i_stat));
+	printf("ProfileMe PCTR_CTL:\t%016llx VAL %d TAK %d Stalled %d Killed %d",
+	       ctl, (int)PCTR_CTL_VAL(ctl), (int)PCTR_CTL_TAK(ctl),
+	       (int)PCTR_CTL_STALLED(ctl), (int)PCTR_CTL_KILLED(ctl));
+	printf(" SL0 %d SL1 %d PCTR0 %d PCTR1 %d (%s)\n",
+	       (int)PCTR_CTL_SL0(ctl), (int)PCTR_CTL_SL1(ctl),
+	       (int)PCTR_CTL_PCTR0(ctl), (int)PCTR_CTL_PCTR1(ctl),
+	       pctr1_names[PCTR_CTL_SL1(ctl)]);
+}
diff --git a/tools/perf/util/sample-raw.c b/tools/perf/util/sample-raw.c
index f5ae9f468983..f765429a481d 100644
--- a/tools/perf/util/sample-raw.c
+++ b/tools/perf/util/sample-raw.c
@@ -19,6 +19,8 @@ void evlist__init_trace_event_sample_raw(struct evlist *evlist, struct perf_env
 
 	if (e_machine == EM_S390) {
 		evlist__set_trace_event_sample_raw(evlist, evlist__s390_sample_raw);
+	} else if (e_machine == EM_ALPHA) {
+		evlist__set_trace_event_sample_raw(evlist, evlist__alpha_sample_raw);
 	} else if (e_machine == EM_X86_64 || e_machine == EM_386) {
 		const char *cpuid = perf_env__cpuid(env);
 
diff --git a/tools/perf/util/sample-raw.h b/tools/perf/util/sample-raw.h
index c8d38c841c8c..8df0bd3d02aa 100644
--- a/tools/perf/util/sample-raw.h
+++ b/tools/perf/util/sample-raw.h
@@ -14,6 +14,8 @@ void evlist__s390_sample_raw(struct evlist *evlist, union perf_event *event,
 bool evlist__has_amd_ibs(struct evlist *evlist);
 void evlist__amd_sample_raw(struct evlist *evlist, union perf_event *event,
 			    struct perf_sample *sample);
+void evlist__alpha_sample_raw(struct evlist *evlist, union perf_event *event,
+			      struct perf_sample *sample);
 void evlist__init_trace_event_sample_raw(struct evlist *evlist, struct perf_env *env);
 
 #endif /* __SAMPLE_RAW_H */

-- 
2.55.0

[PATCH v2 2/2] perf python: Add alpha-profileme.py

[Matt Turner]

perf report shows where Alpha ProfileMe samples land but cannot
aggregate the raw status attached to them.

Add a standalone script, using the perf Python module, that summarizes
it by symbol or, with --pc, by instruction, in the style of DCPI: the
fraction of samples killed on a wrong path, not retired, mispredicted,
taken or stalled, the mean PCTR1 window count, and trap counts by type.
Mispredict and trap types are only counted when I_STAT[TRP] is set,
since they are stale otherwise. Redirect traps are counted by their
PALcode entry offset in PMPC.

On an EV7, sampling a loop whose branch tests random data reports that
branch mispredicted in 21% of its samples, and 0% with sorted data.

Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 tools/perf/python/alpha-profileme.py | 162 +++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)

diff --git a/tools/perf/python/alpha-profileme.py b/tools/perf/python/alpha-profileme.py
new file mode 100755
index 000000000000..19572431aeac
--- /dev/null
+++ b/tools/perf/python/alpha-profileme.py
@@ -0,0 +1,162 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+"""Summarize Alpha ProfileMe samples.
+
+Aggregates the ProfileMe status that the Alpha cpu PMU attaches to each
+sample as PERF_SAMPLE_RAW data, by symbol or, with --pc, by instruction.
+
+Record with raw data, e.g.:
+  perf record -R -e instructions:p -- ./workload
+  alpha-profileme.py [-i perf.data] [--pc] [--top N]
+
+Columns:
+  samples   ProfileMe samples attributed to the row
+  killed%   profiled instruction killed before it was mapped (PM_KILLED_BM)
+  invalid%  instruction did not trap and did not retire valid (VAL clear)
+  mispr%    conditional branch mispredicted (TRP and MIS)
+  taken%    TAK set; only meaningful for rows that are conditional branches
+  stall%    instruction stalled between fetch and map (PM_STALLED)
+  pctr1     mean PCTR1 count during the window; what it counts depends on
+            the event: inum retire delay for cycles:p, window cycles for
+            instructions:p, Bcache misses for bcache-misses:p and Mbox
+            replay traps for cpu/mbox-replay/p
+  traps     trap counts by type, only for samples with TRP set
+"""
+from __future__ import annotations
+
+import argparse
+from collections import defaultdict
+import struct
+import sys
+from typing import Optional
+import perf
+
+TRAP_TYPES = {
+    0: "replay", 2: "dtb2-3l", 3: "dtb2-4l", 4: "fen", 5: "unalign",
+    6: "dtb1", 7: "dfault", 8: "opcdec", 10: "mchk", 12: "arith",
+    14: "mt_fpcr", 15: "reset",
+}
+REDIRECTS = {0x481: "iacv", 0x581: "itbmiss", 0x681: "intr"}
+SAMPLE = struct.Struct("<IQQQ")
+
+
+class Row:
+    """ProfileMe status totals for one symbol or instruction."""
+    def __init__(self) -> None:
+        self.samples = 0
+        self.killed = 0
+        self.invalid = 0
+        self.mispredict = 0
+        self.taken = 0
+        self.stalled = 0
+        self.pctr1 = 0
+        self.traps: dict[str, int] = defaultdict(int)
+
+
+def pct(n: int, d: int) -> float:
+    """Return n as a percentage of d."""
+    return 100.0 * n / d if d else 0.0
+
+
+class ProfileMe:
+    """Aggregates ProfileMe raw sample data."""
+    def __init__(self, by_pc: bool, top: int) -> None:
+        self.by_pc = by_pc
+        self.top = top
+        self.rows: dict[str, Row] = defaultdict(Row)
+        self.skipped = 0
+        self.session: Optional[perf.session] = None
+
+    def process_event(self, sample: perf.sample_event) -> None:
+        """Add one sample's ProfileMe status to its row."""
+        raw = sample.raw_buf
+        if not raw or len(raw) < SAMPLE.size:
+            self.skipped += 1
+            return
+        version, pmpc, i_stat, ctl = SAMPLE.unpack_from(raw)
+        if version < 1:
+            self.skipped += 1
+            return
+
+        symbol = sample.symbol or "[unknown]"
+        if self.by_pc:
+            if pmpc & 1:
+                key = f"PAL+{pmpc & 0x7fff:#x}"
+            else:
+                key = f"{pmpc & ~3:#018x} {symbol}"
+        else:
+            key = f"{sample.dso or '[unknown]'} {symbol}"
+
+        r = self.rows[key]
+        r.samples += 1
+        trp = (i_stat >> 39) & 1
+        if (ctl >> 26) & 1:
+            r.killed += 1
+        if not trp and not (ctl >> 1) & 1:
+            r.invalid += 1
+        if ctl & 1:
+            r.taken += 1
+        if (ctl >> 27) & 1:
+            r.stalled += 1
+        r.pctr1 += (ctl >> 6) & 0xfffff
+
+        redirect = REDIRECTS.get(pmpc & 0x7fff) if pmpc & 1 else None
+        if redirect:
+            r.traps[redirect] += 1
+        elif trp:
+            if (i_stat >> 40) & 1:
+                r.mispredict += 1
+            else:
+                tt = (i_stat >> 34) & 0xf
+                r.traps[TRAP_TYPES.get(tt, "other")] += 1
+
+    def print_totals(self) -> None:
+        """Print the busiest rows."""
+        total = sum(r.samples for r in self.rows.values())
+        print(f"{total} ProfileMe samples, {self.skipped} without ProfileMe data")
+        if not total:
+            return
+        print(f"{'samples':>8} {'killed%':>7} {'invalid%':>8} {'mispr%':>6} "
+              f"{'taken%':>7} {'stall%':>6} {'pctr1':>7}  {'location':<40} traps")
+        ordered = sorted(self.rows.items(), key=lambda kv: kv[1].samples,
+                         reverse=True)
+        for key, r in ordered[:self.top]:
+            traps = " ".join(f"{k}={v}" for k, v in
+                             sorted(r.traps.items(), key=lambda kv: -kv[1]))
+            print(f"{r.samples:8d} {pct(r.killed, r.samples):7.1f} "
+                  f"{pct(r.invalid, r.samples):8.1f} "
+                  f"{pct(r.mispredict, r.samples):6.1f} "
+                  f"{pct(r.taken, r.samples):7.1f} "
+                  f"{pct(r.stalled, r.samples):6.1f} "
+                  f"{r.pctr1 / r.samples:7.1f}  {key:<40} {traps}")
+
+    def run(self, input_file: str) -> None:
+        """Run the session."""
+        self.session = perf.session(perf.data(input_file), sample=self.process_event)
+        try:
+            self.session.process_events()
+        finally:
+            # Break the reference cycle between perf.session and self.process_event
+            # because perf.session lacks cyclic GC support (tp_traverse).
+            self.session = None
+        self.print_totals()
+
+
+def main() -> None:
+    """Main function."""
+    parser = argparse.ArgumentParser(description="Summarize Alpha ProfileMe samples")
+    parser.add_argument("-i", "--input", default="perf.data", help="Input file")
+    parser.add_argument("--pc", action="store_true", help="aggregate by instruction")
+    parser.add_argument("--top", type=int, default=30, help="rows to print")
+    args = parser.parse_args()
+
+    analyzer = ProfileMe(args.pc, args.top)
+    try:
+        analyzer.run(args.input)
+    except IOError as e:
+        print(e, file=sys.stderr)
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()

-- 
2.55.0

Re: [PATCH v2 2/2] perf python: Add alpha-profileme.py

[sashiko-bot]

> perf report shows where Alpha ProfileMe samples land but cannot
> aggregate the raw status attached to them.
> 
> Add a standalone script, using the perf Python module, that summarizes
> it by symbol or, with --pc, by instruction, in the style of DCPI: the
> fraction of samples killed on a wrong path, not retired, mispredicted,
> taken or stalled, the mean PCTR1 window count, and trap counts by type.
> Mispredict and trap types are only counted when I_STAT[TRP] is set,
> since they are stale otherwise. Redirect traps are counted by their
> PALcode entry offset in PMPC.
> 
> On an EV7, sampling a loop whose branch tests random data reports that
> branch mispredicted in 21% of its samples, and 0% with sorted data.
> 
> Signed-off-by: Matt Turner <mattst88@gmail.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261030-perf-alpha-profileme-v2-0-9ce2f0b0e622@gmail.com?part=2

Re: [PATCH v2 1/2] perf alpha: Decode ProfileMe raw samples

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] perf alpha: missing -Wpacked suppression breaks build on 32-bit targets
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commit 119dd432f8c77b285bd2a318dab7adc61639a02f
Author: Matt Turner <mattst88@gmail.com>

perf alpha: Decode ProfileMe raw samples

This commit decodes Alpha ProfileMe PERF_SAMPLE_RAW payloads in perf report
-D and perf script -D, and copies the UAPI header defining struct
alpha_profileme_sample into tools/arch.

> diff --git a/tools/arch/alpha/include/uapi/asm/perf_event.h b/tools/arch/alpha/include/uapi/asm/perf_event.h
> new file mode 100644
> index 0000000000000..aa0eff5a917cb
> --- /dev/null
> +++ b/tools/arch/alpha/include/uapi/asm/perf_event.h
> @@ -0,0 +1,31 @@

[ ... ]

> +#define ALPHA_PROFILEME_SAMPLE_VERSION	1
> +
> +struct alpha_profileme_sample {
> +	__u32 version;
> +	__u64 pmpc __attribute__((packed));
> +	__u64 i_stat __attribute__((packed));
> +	__u64 pctr_ctl __attribute__((packed));
> +};
> +
> +#endif /* _UAPI_ASM_ALPHA_PERF_EVENT_H */

[ ... ]

> diff --git a/tools/perf/util/alpha-sample-raw.c b/tools/perf/util/alpha-sample-raw.c
> new file mode 100644
> index 0000000000000..b4e336d8fc8f6
> --- /dev/null
> +++ b/tools/perf/util/alpha-sample-raw.c
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Alpha specific. Provide textual annotation for ProfileMe raw sample data.
> + */
> +
> +#include <stdio.h>
> +#include <string.h>
> +#include <linux/kernel.h>
> +#include <linux/perf_event.h>
> +
> +#include "../../arch/alpha/include/uapi/asm/perf_event.h"

[Severity: Low]
Will including this header without suppressing -Wpacked break the build on
32-bit architectures where the natural alignment of __u64 is 32 bits or less
(such as m68k, sh, arc, and microblaze)?

tools/perf/util/Build unconditionally compiles alpha-sample-raw.o on all
architectures with EXTRA_WARNINGS += -Wpacked (in
tools/scripts/Makefile.include) and CORE_CFLAGS += -Werror (in
tools/perf/Makefile.config).

In struct alpha_profileme_sample, the pmpc, i_stat, and pctr_ctl fields sit at
4-byte-aligned offsets after __u32 version and carry __attribute__((packed)),
which lowers their alignment to 1 byte. On targets where __u64 has 4-byte or
smaller alignment, those fields are already naturally aligned at offset 4, so
GCC emits a -Wpacked warning ("packed attribute causes inefficient alignment"),
failing the build under -Werror.

Should the header inclusion in tools/perf/util/alpha-sample-raw.c be wrapped in
diagnostic pragmas, similar to struct pai_data in
tools/perf/util/s390-sample-raw.c:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpacked"
#pragma GCC diagnostic ignored "-Wattributes"
#include "../../arch/alpha/include/uapi/asm/perf_event.h"
#pragma GCC diagnostic pop

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261030-perf-alpha-profileme-v2-0-9ce2f0b0e622@gmail.com?part=1