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perf mem record: Request PERF_SAMPLE_CPU by default

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The data type profiling per-sample stream keys cross-CPU contention on
sample->cpu, which without PERF_SAMPLE_CPU is the "no CPU info"
sentinel, making same-instance accesses from different cores
indistinguishable from same-CPU traffic.  'perf mem record' already
passes -d and -W to the record parser, add --sample-cpu and document it
in perf-mem(1).

Also grow rec_argv: the new entry overflows it on PMUs with separate
load and store events, as the space for the fixed arguments was not
reserved.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Assisted-by: LLM
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2026-09-24 16:27:57 -03:00
parent 02ee4666a0
commit 010147f87a
2 changed files with 9 additions and 2 deletions
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4
tools/perf/Documentation/perf-mem.txt
View File

@ -14,6 +14,10 @@ DESCRIPTION
-----------
"perf mem record" runs a command and gathers memory operation data
from it, into perf.data. Perf record options are accepted and are passed through.
It also requests the address (-d), the weight (-W, where supported) and the
CPU id (--sample-cpu) of every sampled access by default; the CPU id is what
lets per-sample analysis tell reads and writes to the same data from
different cores apart from same-CPU traffic.
"perf mem report" displays the result. It invokes perf report with the
right set of options to display a memory access profile. By default, loads

7
tools/perf/builtin-mem.c
View File

@ -99,8 +99,8 @@ static int __cmd_record(int argc, const char **argv, struct perf_mem *mem,
argc = parse_options(argc, argv, options, record_usage,
PARSE_OPT_KEEP_UNKNOWN);
/* Max number of arguments multiplied by number of PMUs that can support them. */
rec_argc = argc + 9 * (perf_pmu__mem_events_num_mem_pmus(pmu) + 1);
/* Max number of arguments per PMU plus the fixed ones added below. */
rec_argc = argc + 8 + 9 * (perf_pmu__mem_events_num_mem_pmus(pmu) + 1);
if (mem->cpu_list)
rec_argc += 2;
@ -135,6 +135,9 @@ static int __cmd_record(int argc, const char **argv, struct perf_mem *mem,
rec_argv[i++] = "-d";
/* Cross-CPU contention keys on sample->cpu, -1 without PERF_SAMPLE_CPU. */
rec_argv[i++] = "--sample-cpu";
if (mem->phys_addr)
rec_argv[i++] = "--phys-data";