Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps

From: Adrian Hunter
Date: Fri Nov 15 2013 - 05:53:37 EST

On 15/11/13 08:06, Ingo Molnar wrote:
>
> * Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxx> wrote:
>
>> +--force-per-cpu::
>> + Force the use of per-cpu mmaps. By default, when tasks are specified (i.e. -p,
>> + -t or -u options) per-thread mmaps are created. This option overrides that and
>> + forces per-cpu mmaps. A side-effect of that is that inheritance is
>> + automatically enabled. Add the -i option also to disable inheritance.
>
> So I still haven't seen an explanation why it's called 'force'
> anything. AFAICS nothing is 'forced' really, this is simply another
> trace-ringbuffer setup method, right?

The option itself does not determine whether or not per-cpu mmaps are used.
For example you cannot get a per-thread mmap for a workload by:

perf record --no-force-per-cpu ls

So the option, as implemented, is a modifier of other options, not an option
in itself. That is why its called 'force'.

To drop 'force':




From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Date: Fri, 15 Nov 2013 09:40:00 +0200
Subject: [PATCH] perf record: Drop 'force' from --force-per-cpu option

'force' is confusing so rename the option and
change the documentation accordingly.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
tools/perf/Documentation/perf-record.txt | 10 +++++-----
tools/perf/builtin-record.c | 4 ++--
2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 43b42c4..98a7d66 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -201,11 +201,11 @@ abort events and some memory events in precise mode on modern Intel CPUs.
--transaction::
Record transaction flags for transaction related events.

---force-per-cpu::
-Force the use of per-cpu mmaps. By default, when tasks are specified (i.e. -p,
--t or -u options) per-thread mmaps are created. This option overrides that and
-forces per-cpu mmaps. A side-effect of that is that inheritance is
-automatically enabled. Add the -i option also to disable inheritance.
+--per-cpu::
+Use per-cpu mmaps. By default, when tasks are specified (i.e. -p, -t or -u
+options) per-thread mmaps are created. This option overrides that and uses
+per-cpu mmaps. A side-effect of that is that inheritance is automatically
+enabled. Add the -i option also to disable inheritance.

SEE ALSO
--------
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 7c8020a..56ca57d 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -888,8 +888,8 @@ const struct option record_options[] = {
"sample by weight (on special events only)"),
OPT_BOOLEAN(0, "transaction", &record.opts.sample_transaction,
"sample transaction flags (special events only)"),
- OPT_BOOLEAN(0, "force-per-cpu", &record.opts.target.force_per_cpu,
- "force the use of per-cpu mmaps"),
+ OPT_BOOLEAN(0, "per-cpu", &record.opts.target.force_per_cpu,
+ "use per-cpu mmaps"),
OPT_END()
};

--
1.7.11.7




But really then --no-per-cpu needs to be implemented:




From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Date: Fri, 15 Nov 2013 10:26:50 +0200
Subject: [PATCH 2/2] perf record: Allow --no-per-cpu to select per-thread
mmaps

The effect of --no-per-cpu is:

-p, -t, -u no difference
-C, -a no difference (causes a
warning)
otherwise record the workload as a
single thread i.e.
no-inheritance

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
tools/perf/builtin-record.c | 20 ++++++++++++++++++--
tools/perf/util/evlist.c | 2 +-
tools/perf/util/target.c | 11 ++++++++++-
tools/perf/util/target.h | 2 ++
4 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 56ca57d..d2dbb01 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -776,6 +776,22 @@ int record_callchain_opt(const struct option *opt,
return 0;
}

+static int parse_per_cpu(const struct option *opt,
+ const char *arg __maybe_unused, int unset)
+{
+ struct target *target = opt->value;
+
+ if (unset) {
+ target->force_per_cpu = false;
+ target->force_per_thread = true;
+ } else {
+ target->force_per_cpu = true;
+ target->force_per_thread = false;
+ }
+
+ return 0;
+}
+
static const char * const record_usage[] = {
"perf record [<options>] [<command>]",
"perf record [<options>] -- <command> [<options>]",
@@ -888,8 +904,8 @@ const struct option record_options[] = {
"sample by weight (on special events only)"),
OPT_BOOLEAN(0, "transaction", &record.opts.sample_transaction,
"sample transaction flags (special events only)"),
- OPT_BOOLEAN(0, "per-cpu", &record.opts.target.force_per_cpu,
- "use per-cpu mmaps"),
+ OPT_CALLBACK_NOOPT(0, "per-cpu", &record.opts.target, "per-cpu",
+ "use per-cpu mmaps", parse_per_cpu),
OPT_END()
};

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index bbc746a..3ed4674 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -821,7 +821,7 @@ int perf_evlist__create_maps(struct perf_evlist *evlist, struct target *target)

if (target->force_per_cpu)
evlist->cpus = cpu_map__new(target->cpu_list);
- else if (target__has_task(target))
+ else if (target__has_task(target) || target->force_per_thread)
evlist->cpus = cpu_map__dummy_new();
else if (!target__has_cpu(target) && !target->uses_mmap)
evlist->cpus = cpu_map__dummy_new();
diff --git a/tools/perf/util/target.c b/tools/perf/util/target.c
index 3c778a0..11d4527 100644
--- a/tools/perf/util/target.c
+++ b/tools/perf/util/target.c
@@ -55,6 +55,13 @@ enum target_errno target__validate(struct target *target)
ret = TARGET_ERRNO__UID_OVERRIDE_SYSTEM;
}

+ if (target->force_per_thread &&
+ (target->system_wide || target->cpu_list)) {
+ target->force_per_thread = false;
+ if (ret == TARGET_ERRNO__SUCCESS)
+ ret = TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD;
+ }
+
return ret;
}

@@ -100,6 +107,7 @@ static const char *target__error_str[] = {
"UID switch overriding CPU",
"PID/TID switch overriding SYSTEM",
"UID switch overriding SYSTEM",
+ "SYSTEM/CPU switch overriding NO-PER-CPU",
"Invalid User: %s",
"Problems obtaining information for user %s",
};
@@ -131,7 +139,8 @@ int target__strerror(struct target *target, int errnum,
msg = target__error_str[idx];

switch (errnum) {
- case TARGET_ERRNO__PID_OVERRIDE_CPU ... TARGET_ERRNO__UID_OVERRIDE_SYSTEM:
+ case TARGET_ERRNO__PID_OVERRIDE_CPU ...
+ TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD:
snprintf(buf, buflen, "%s", msg);
break;

diff --git a/tools/perf/util/target.h b/tools/perf/util/target.h
index 2d0c506..65494c1b 100644
--- a/tools/perf/util/target.h
+++ b/tools/perf/util/target.h
@@ -13,6 +13,7 @@ struct target {
bool system_wide;
bool uses_mmap;
bool force_per_cpu;
+ bool force_per_thread;
};

enum target_errno {
@@ -33,6 +34,7 @@ enum target_errno {
TARGET_ERRNO__UID_OVERRIDE_CPU,
TARGET_ERRNO__PID_OVERRIDE_SYSTEM,
TARGET_ERRNO__UID_OVERRIDE_SYSTEM,
+ TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD,

/* for target__parse_uid() */
TARGET_ERRNO__INVALID_UID,
--
1.7.11.7




>
> And I also raised why this shouldn't be the default event tracing
> method instead of a weird config option. Per-cpu tracing is cache
> compact, it is easier to size properly and in general it is pretty
> easy to think about. (It also has less of the TSC timestamp ordering
> problems as per thread tracing, at least in theory.)
>
> Is there something that makes per cpu tracing undesirable as the
> default?

One reason is to avoid changing the meaning of existing options.

To flip it around, ignore the patches above and apply:



From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Date: Fri, 15 Nov 2013 11:17:56 +0200
Subject: [PATCH] perf record: Make per-cpu mmaps the default.

This affects the -p, -t and -u options that
previously defaulted to per-thread mmaps.

Consequently add an option to select
per-thread mmaps to support the old
behaviour.

Note that per-thread can be used with a
workload-only (i.e. none of -p, -t, -u,
-a or -C is selected) to get a per-thread
mmap with no inheritance.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
tools/perf/Documentation/perf-record.txt | 10 +++++-----
tools/perf/builtin-record.c | 5 +++--
tools/perf/util/evlist.c | 6 ++++--
tools/perf/util/evsel.c | 4 ++--
tools/perf/util/target.c | 11 ++++++++++-
tools/perf/util/target.h | 4 +++-
6 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 43b42c4..6ac867e 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -201,11 +201,11 @@ abort events and some memory events in precise mode on modern Intel CPUs.
--transaction::
Record transaction flags for transaction related events.

---force-per-cpu::
-Force the use of per-cpu mmaps. By default, when tasks are specified (i.e. -p,
--t or -u options) per-thread mmaps are created. This option overrides that and
-forces per-cpu mmaps. A side-effect of that is that inheritance is
-automatically enabled. Add the -i option also to disable inheritance.
+--per-thread::
+Use per-thread mmaps. By default per-cpu mmaps are created. This option
+overrides that and uses per-thread mmaps. A side-effect of that is that
+inheritance is automatically disabled. --per-thread is ignored with a warning
+if combined with -a or -C options.

SEE ALSO
--------
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 7c8020a..f5b18b8 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -800,6 +800,7 @@ static struct perf_record record = {
.freq = 4000,
.target = {
.uses_mmap = true,
+ .default_per_cpu = true,
},
},
};
@@ -888,8 +889,8 @@ const struct option record_options[] = {
"sample by weight (on special events only)"),
OPT_BOOLEAN(0, "transaction", &record.opts.sample_transaction,
"sample transaction flags (special events only)"),
- OPT_BOOLEAN(0, "force-per-cpu", &record.opts.target.force_per_cpu,
- "force the use of per-cpu mmaps"),
+ OPT_BOOLEAN(0, "per-thread", &record.opts.target.per_thread,
+ "use per-thread mmaps"),
OPT_END()
};

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index bbc746a..76fa764 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -819,8 +819,10 @@ int perf_evlist__create_maps(struct perf_evlist *evlist, struct target *target)
if (evlist->threads == NULL)
return -1;

- if (target->force_per_cpu)
- evlist->cpus = cpu_map__new(target->cpu_list);
+ if (target->default_per_cpu)
+ evlist->cpus = target->per_thread ?
+ cpu_map__dummy_new() :
+ cpu_map__new(target->cpu_list);
else if (target__has_task(target))
evlist->cpus = cpu_map__dummy_new();
else if (!target__has_cpu(target) && !target->uses_mmap)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 46dd4c2..18f7c18 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -645,7 +645,7 @@ void perf_evsel__config(struct perf_evsel *evsel,
}
}

- if (target__has_cpu(&opts->target) || opts->target.force_per_cpu)
+ if (target__has_cpu(&opts->target))
perf_evsel__set_sample_bit(evsel, CPU);

if (opts->period)
@@ -653,7 +653,7 @@ void perf_evsel__config(struct perf_evsel *evsel,

if (!perf_missing_features.sample_id_all &&
(opts->sample_time || !opts->no_inherit ||
- target__has_cpu(&opts->target) || opts->target.force_per_cpu))
+ target__has_cpu(&opts->target)))
perf_evsel__set_sample_bit(evsel, TIME);

if (opts->raw_samples) {
diff --git a/tools/perf/util/target.c b/tools/perf/util/target.c
index 3c778a0..e74c596 100644
--- a/tools/perf/util/target.c
+++ b/tools/perf/util/target.c
@@ -55,6 +55,13 @@ enum target_errno target__validate(struct target *target)
ret = TARGET_ERRNO__UID_OVERRIDE_SYSTEM;
}

+ /* THREAD and SYSTEM/CPU are mutually exclusive */
+ if (target->per_thread && (target->system_wide || target->cpu_list)) {
+ target->per_thread = false;
+ if (ret == TARGET_ERRNO__SUCCESS)
+ ret = TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD;
+ }
+
return ret;
}

@@ -100,6 +107,7 @@ static const char *target__error_str[] = {
"UID switch overriding CPU",
"PID/TID switch overriding SYSTEM",
"UID switch overriding SYSTEM",
+ "SYSTEM/CPU switch overriding PER-THREAD",
"Invalid User: %s",
"Problems obtaining information for user %s",
};
@@ -131,7 +139,8 @@ int target__strerror(struct target *target, int errnum,
msg = target__error_str[idx];

switch (errnum) {
- case TARGET_ERRNO__PID_OVERRIDE_CPU ... TARGET_ERRNO__UID_OVERRIDE_SYSTEM:
+ case TARGET_ERRNO__PID_OVERRIDE_CPU ...
+ TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD:
snprintf(buf, buflen, "%s", msg);
break;

diff --git a/tools/perf/util/target.h b/tools/perf/util/target.h
index 2d0c506..31dd2e9 100644
--- a/tools/perf/util/target.h
+++ b/tools/perf/util/target.h
@@ -12,7 +12,8 @@ struct target {
uid_t uid;
bool system_wide;
bool uses_mmap;
- bool force_per_cpu;
+ bool default_per_cpu;
+ bool per_thread;
};

enum target_errno {
@@ -33,6 +34,7 @@ enum target_errno {
TARGET_ERRNO__UID_OVERRIDE_CPU,
TARGET_ERRNO__PID_OVERRIDE_SYSTEM,
TARGET_ERRNO__UID_OVERRIDE_SYSTEM,
+ TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD,

/* for target__parse_uid() */
TARGET_ERRNO__INVALID_UID,
--
1.7.11.7





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