Re: [PATCH v8 03/22] perf record: Introduce thread local variable

[Bayduraev, Alexey V]

Hi,

On 30.06.2021 20:16, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 30, 2021 at 06:54:42PM +0300, Alexey Bayduraev escreveu:
>> Introduce thread local variable and use it for threaded trace streaming.
[SNIP]
>>  static void record__adjust_affinity(struct record *rec, struct mmap *map)
>>  {
>> +	int ret = 0;
> 
> Why you set this to zero here if it is going to be used only insde the
> if block?
> 
>> +
>>  	if (rec->opts.affinity != PERF_AFFINITY_SYS &&
>> -	    !bitmap_equal(rec->affinity_mask.bits, map->affinity_mask.bits,
>> -			  rec->affinity_mask.nbits)) {
>> -		bitmap_zero(rec->affinity_mask.bits, rec->affinity_mask.nbits);
>> -		bitmap_or(rec->affinity_mask.bits, rec->affinity_mask.bits,
>> -			  map->affinity_mask.bits, rec->affinity_mask.nbits);
>> -		sched_setaffinity(0, MMAP_CPU_MASK_BYTES(&rec->affinity_mask),
>> -				  (cpu_set_t *)rec->affinity_mask.bits);
>> -		if (verbose == 2)
>> -			mmap_cpu_mask__scnprintf(&rec->affinity_mask, "thread");
>> +	    !bitmap_equal(thread->mask->affinity.bits, map->affinity_mask.bits,
>> +			  thread->mask->affinity.nbits)) {
>> +		bitmap_zero(thread->mask->affinity.bits, thread->mask->affinity.nbits);
>> +		bitmap_or(thread->mask->affinity.bits, thread->mask->affinity.bits,
>> +			  map->affinity_mask.bits, thread->mask->affinity.nbits);
>> +		ret = sched_setaffinity(0, MMAP_CPU_MASK_BYTES(&thread->mask->affinity),
>> +					(cpu_set_t *)thread->mask->affinity.bits);
>> +		if (ret)
>> +			pr_err("threads[%d]: sched_setaffinity() call failed: %s\n",
>> +			       thread->tid, strerror(errno));
> 
> Also, if record__adjust_affinity() fails by means of sched_setaffinity
> not working, shouldn't we propagate this error?
> 

I am also in doubt. record__adjust_affinity() is called inside mmap read
function and I don't think it's a good idea to terminate the data
collection in the middle. I guess this can be critical only for real-time
workloads.

Regards,
Alexey

>> +		if (verbose == 2) {
>> +			pr_debug("threads[%d]: addr=", thread->tid);
>> +			mmap_cpu_mask__scnprintf(&thread->mask->affinity, "thread");
>> +			pr_debug("threads[%d]: on cpu=%d\n", thread->tid, sched_getcpu());
>> +		}
>>  	}
>>  }
>>  
>> @@ -1310,14 +1319,17 @@ static int record__mmap_read_evlist(struct record *rec, struct evlist *evlist,
>>  	u64 bytes_written = rec->bytes_written;
>>  	int i;
>>  	int rc = 0;
>> -	struct mmap *maps;
>> +	int nr_mmaps;
>> +	struct mmap **maps;
>>  	int trace_fd = rec->data.file.fd;
>>  	off_t off = 0;
>>  
>>  	if (!evlist)
>>  		return 0;
>>  
>> -	maps = overwrite ? evlist->overwrite_mmap : evlist->mmap;
>> +	nr_mmaps = thread->nr_mmaps;
>> +	maps = overwrite ? thread->overwrite_maps : thread->maps;
>> +
>>  	if (!maps)
>>  		return 0;
>>  
>> @@ -1327,9 +1339,9 @@ static int record__mmap_read_evlist(struct record *rec, struct evlist *evlist,
>>  	if (record__aio_enabled(rec))
>>  		off = record__aio_get_pos(trace_fd);
>>  
>> -	for (i = 0; i < evlist->core.nr_mmaps; i++) {
>> +	for (i = 0; i < nr_mmaps; i++) {
>>  		u64 flush = 0;
>> -		struct mmap *map = &maps[i];
>> +		struct mmap *map = maps[i];
>>  
>>  		if (map->core.base) {
>>  			record__adjust_affinity(rec, map);
>> @@ -1392,6 +1404,15 @@ static int record__mmap_read_all(struct record *rec, bool synch)
>>  	return record__mmap_read_evlist(rec, rec->evlist, true, synch);
>>  }
>>  
>> +static void record__thread_munmap_filtered(struct fdarray *fda, int fd,
>> +					   void *arg __maybe_unused)
>> +{
>> +	struct perf_mmap *map = fda->priv[fd].ptr;
>> +
>> +	if (map)
>> +		perf_mmap__put(map);
>> +}
>> +
>>  static void record__init_features(struct record *rec)
>>  {
>>  	struct perf_session *session = rec->session;
>> @@ -1836,6 +1857,33 @@ static void record__uniquify_name(struct record *rec)
>>  	}
>>  }
>>  
>> +static int record__start_threads(struct record *rec)
>> +{
>> +	struct thread_data *thread_data = rec->thread_data;
>> +
>> +	thread = &thread_data[0];
>> +
>> +	pr_debug("threads[%d]: started on cpu=%d\n", thread->tid, sched_getcpu());
>> +
>> +	return 0;
>> +}
>> +
>> +static int record__stop_threads(struct record *rec, unsigned long *waking)
>> +{
>> +	int t;
>> +	struct thread_data *thread_data = rec->thread_data;
>> +
>> +	for (t = 0; t < rec->nr_threads; t++) {
>> +		rec->samples += thread_data[t].samples;
>> +		*waking += thread_data[t].waking;
>> +		pr_debug("threads[%d]: samples=%lld, wakes=%ld, trasferred=%ld, compressed=%ld\n",
>> +			 thread_data[t].tid, thread_data[t].samples, thread_data[t].waking,
>> +			 rec->session->bytes_transferred, rec->session->bytes_compressed);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  {
>>  	int err;
>> @@ -1944,7 +1992,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  
>>  	if (record__open(rec) != 0) {
>>  		err = -1;
>> -		goto out_child;
>> +		goto out_free_threads;
>>  	}
>>  	session->header.env.comp_mmap_len = session->evlist->core.mmap_len;
>>  
>> @@ -1952,7 +2000,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  		err = record__kcore_copy(&session->machines.host, data);
>>  		if (err) {
>>  			pr_err("ERROR: Failed to copy kcore\n");
>> -			goto out_child;
>> +			goto out_free_threads;
>>  		}
>>  	}
>>  
>> @@ -1963,7 +2011,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  		bpf__strerror_apply_obj_config(err, errbuf, sizeof(errbuf));
>>  		pr_err("ERROR: Apply config to BPF failed: %s\n",
>>  			 errbuf);
>> -		goto out_child;
>> +		goto out_free_threads;
>>  	}
>>  
>>  	/*
>> @@ -1981,11 +2029,11 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  	if (data->is_pipe) {
>>  		err = perf_header__write_pipe(fd);
>>  		if (err < 0)
>> -			goto out_child;
>> +			goto out_free_threads;
>>  	} else {
>>  		err = perf_session__write_header(session, rec->evlist, fd, false);
>>  		if (err < 0)
>> -			goto out_child;
>> +			goto out_free_threads;
>>  	}
>>  
>>  	err = -1;
>> @@ -1993,16 +2041,16 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  	    && !perf_header__has_feat(&session->header, HEADER_BUILD_ID)) {
>>  		pr_err("Couldn't generate buildids. "
>>  		       "Use --no-buildid to profile anyway.\n");
>> -		goto out_child;
>> +		goto out_free_threads;
>>  	}
>>  
>>  	err = record__setup_sb_evlist(rec);
>>  	if (err)
>> -		goto out_child;
>> +		goto out_free_threads;
>>  
>>  	err = record__synthesize(rec, false);
>>  	if (err < 0)
>> -		goto out_child;
>> +		goto out_free_threads;
>>  
>>  	if (rec->realtime_prio) {
>>  		struct sched_param param;
>> @@ -2011,10 +2059,13 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  		if (sched_setscheduler(0, SCHED_FIFO, &param)) {
>>  			pr_err("Could not set realtime priority.\n");
>>  			err = -1;
>> -			goto out_child;
>> +			goto out_free_threads;
>>  		}
>>  	}
>>  
>> +	if (record__start_threads(rec))
>> +		goto out_free_threads;
>> +
>>  	/*
>>  	 * When perf is starting the traced process, all the events
>>  	 * (apart from group members) have enable_on_exec=1 set,
>> @@ -2085,7 +2136,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  	trigger_ready(&switch_output_trigger);
>>  	perf_hooks__invoke_record_start();
>>  	for (;;) {
>> -		unsigned long long hits = rec->samples;
>> +		unsigned long long hits = thread->samples;
>>  
>>  		/*
>>  		 * rec->evlist->bkw_mmap_state is possible to be
>> @@ -2154,20 +2205,24 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  				alarm(rec->switch_output.time);
>>  		}
>>  
>> -		if (hits == rec->samples) {
>> +		if (hits == thread->samples) {
>>  			if (done || draining)
>>  				break;
>> -			err = evlist__poll(rec->evlist, -1);
>> +			err = fdarray__poll(&thread->pollfd, -1);
>>  			/*
>>  			 * Propagate error, only if there's any. Ignore positive
>>  			 * number of returned events and interrupt error.
>>  			 */
>>  			if (err > 0 || (err < 0 && errno == EINTR))
>>  				err = 0;
>> -			waking++;
>> +			thread->waking++;
>>  
>> -			if (evlist__filter_pollfd(rec->evlist, POLLERR | POLLHUP) == 0)
>> +			if (fdarray__filter(&thread->pollfd, POLLERR | POLLHUP,
>> +					    record__thread_munmap_filtered, NULL) == 0)
>>  				draining = true;
>> +
>> +			evlist__ctlfd_update(rec->evlist,
>> +				&thread->pollfd.entries[thread->ctlfd_pos]);
>>  		}
>>  
>>  		if (evlist__ctlfd_process(rec->evlist, &cmd) > 0) {
>> @@ -2220,18 +2275,20 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  		goto out_child;
>>  	}
>>  
>> -	if (!quiet)
>> -		fprintf(stderr, "[ perf record: Woken up %ld times to write data ]\n", waking);
>> -
>>  	if (target__none(&rec->opts.target))
>>  		record__synthesize_workload(rec, true);
>>  
>>  out_child:
>> -	evlist__finalize_ctlfd(rec->evlist);
>> +	record__stop_threads(rec, &waking);
>>  	record__mmap_read_all(rec, true);
>> +out_free_threads:
>>  	record__free_thread_data(rec);
>> +	evlist__finalize_ctlfd(rec->evlist);
>>  	record__aio_mmap_read_sync(rec);
>>  
>> +	if (!quiet)
>> +		fprintf(stderr, "[ perf record: Woken up %ld times to write data ]\n", waking);
>> +
>>  	if (rec->session->bytes_transferred && rec->session->bytes_compressed) {
>>  		ratio = (float)rec->session->bytes_transferred/(float)rec->session->bytes_compressed;
>>  		session->header.env.comp_ratio = ratio + 0.5;
>> @@ -3093,17 +3150,6 @@ int cmd_record(int argc, const char **argv)
>>  
>>  	symbol__init(NULL);
>>  
>> -	if (rec->opts.affinity != PERF_AFFINITY_SYS) {
>> -		rec->affinity_mask.nbits = cpu__max_cpu();
>> -		rec->affinity_mask.bits = bitmap_alloc(rec->affinity_mask.nbits);
>> -		if (!rec->affinity_mask.bits) {
>> -			pr_err("Failed to allocate thread mask for %zd cpus\n", rec->affinity_mask.nbits);
>> -			err = -ENOMEM;
>> -			goto out_opts;
>> -		}
>> -		pr_debug2("thread mask[%zd]: empty\n", rec->affinity_mask.nbits);
>> -	}
>> -
>>  	err = record__auxtrace_init(rec);
>>  	if (err)
>>  		goto out;
>> @@ -3241,7 +3287,6 @@ int cmd_record(int argc, const char **argv)
>>  
>>  	err = __cmd_record(&record, argc, argv);
>>  out:
>> -	bitmap_free(rec->affinity_mask.bits);
>>  	evlist__delete(rec->evlist);
>>  	symbol__exit();
>>  	auxtrace_record__free(rec->itr);
> 
> 
> Can the following be moved to a separate patch?
> 
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 6ba9664089bd..3d555a98c037 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -2132,6 +2132,22 @@ int evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
>>  	return err;
>>  }
>>  
>> +int evlist__ctlfd_update(struct evlist *evlist, struct pollfd *update)
>> +{
>> +	int ctlfd_pos = evlist->ctl_fd.pos;
>> +	struct pollfd *entries = evlist->core.pollfd.entries;
>> +
>> +	if (!evlist__ctlfd_initialized(evlist))
>> +		return 0;
>> +
>> +	if (entries[ctlfd_pos].fd != update->fd ||
>> +	    entries[ctlfd_pos].events != update->events)
>> +		return -1;
>> +
>> +	entries[ctlfd_pos].revents = update->revents;
>> +	return 0;
>> +}
>> +
>>  struct evsel *evlist__find_evsel(struct evlist *evlist, int idx)
>>  {
>>  	struct evsel *evsel;
>> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
>> index 2073cfa79f79..b7aa719c638d 100644
>> --- a/tools/perf/util/evlist.h
>> +++ b/tools/perf/util/evlist.h
>> @@ -358,6 +358,7 @@ void evlist__close_control(int ctl_fd, int ctl_fd_ack, bool *ctl_fd_close);
>>  int evlist__initialize_ctlfd(struct evlist *evlist, int ctl_fd, int ctl_fd_ack);
>>  int evlist__finalize_ctlfd(struct evlist *evlist);
>>  bool evlist__ctlfd_initialized(struct evlist *evlist);
>> +int evlist__ctlfd_update(struct evlist *evlist, struct pollfd *update);
>>  int evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd);
>>  int evlist__ctlfd_ack(struct evlist *evlist);
>>  
>> -- 
>> 2.19.0
>>
>