Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

[Don Zickus <dzickus@redhat.com>]

On Wed, Mar 25, 2015 at 10:51:10AM -0600, David Ahern wrote:
> 363b785f38 added synthesized fork events and set a thread's parent id
> to itself. Since we are already processing /proc/<pid>/status the ppid
> can be determined properly. Make it so.
> 
> Performance impact measured on a sparc based T5-8 (1024 CPUs):
> $ ps -efL | wc -l
> 20185
> 
> Current code:
> $ time perf record -o perf-no-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> mmap size 532480B
> [ perf record: Woken up 0 times to write data ]
> failed to write feature 9
> [ perf record: Captured and wrote 0.000 MB perf-no-ppid.data ]
> 
> real	0m26.144s
> user	0m0.452s
> sys	0m25.564s
> 
> With PPID patch:
> $ time ./perf_ppid record -o perf-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> mmap size 532480B
> [ perf record: Woken up 0 times to write data ]
> failed to write feature 9
> [ perf record: Captured and wrote 0.000 MB perf-ppid.data ]
> 
> real	0m25.743s
> user	0m0.268s
> sys	0m25.368s
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> Cc: Don Zickus <dzickus@redhat.com>
> Cc: Joe Mario <jmario@redhat.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> ---
> v2:
> - removed loop in place of 1 read and processing a buffer

Hmm, I am not entirely sure this is correct.  You made an optimization that
hides the negative impact your patch does.  I would prefer you split this
patch into two pieces.  One with the read loop optimization (which I think
is great) and the second is your ppid change.

I would then like to redo our test with the first patch applied and then
both patches applied.

I still think something is strange in the sense perf wasn't supposed to read
the /proc filesystem again for threads.  It was supposed to inherit the
thread data from the parent (the original intent and big speed up of my
patch).  I believe your patch breaks that and goes back to reading the /proc
filesystem again. :-(  Though I haven't had a chance to figure out why.

Cheers,
Don



> 
>  tools/perf/util/event.c | 178 ++++++++++++++++++++++++++++++------------------
>  1 file changed, 110 insertions(+), 68 deletions(-)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index d5efa5092ce6..e98cbba56033 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -49,70 +49,115 @@ static struct perf_sample synth_sample = {
>  	.period	   = 1,
>  };
>  
> -static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
> +/*
> + * Assumes that the first 4095 bytes of /proc/pid/stat contains
> + * the comm, tgid and ppid.
> + */
> +static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,
> +				    pid_t *tgid, pid_t *ppid)
>  {
>  	char filename[PATH_MAX];
> -	char bf[BUFSIZ];
> -	FILE *fp;
> -	size_t size = 0;
> -	pid_t tgid = -1;
> +	char bf[4096];
> +	int fd;
> +	size_t size = 0, n;
> +	char *nl, *name, *tgids, *ppids;
> +
> +	*tgid = -1;
> +	*ppid = -1;
>  
>  	snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
>  
> -	fp = fopen(filename, "r");
> -	if (fp == NULL) {
> +	fd = open(filename, O_RDONLY);
> +	if (fd < 0) {
>  		pr_debug("couldn't open %s\n", filename);
> -		return 0;
> +		return -1;
>  	}
>  
> -	while (!comm[0] || (tgid < 0)) {
> -		if (fgets(bf, sizeof(bf), fp) == NULL) {
> -			pr_warning("couldn't get COMM and pgid, malformed %s\n",
> -				   filename);
> -			break;
> -		}
> -
> -		if (memcmp(bf, "Name:", 5) == 0) {
> -			char *name = bf + 5;
> -			while (*name && isspace(*name))
> -				++name;
> -			size = strlen(name) - 1;
> -			if (size >= len)
> -				size = len - 1;
> -			memcpy(comm, name, size);
> -			comm[size] = '\0';
> -
> -		} else if (memcmp(bf, "Tgid:", 5) == 0) {
> -			char *tgids = bf + 5;
> -			while (*tgids && isspace(*tgids))
> -				++tgids;
> -			tgid = atoi(tgids);
> -		}
> +	n = read(fd, bf, sizeof(bf) - 1);
> +	close(fd);
> +	if (n <= 0) {
> +		pr_warning("Couldn't get COMM, tigd and ppid for pid %d\n",
> +			   pid);
> +		return -1;
>  	}
> +	bf[n] = '\0';
>  
> -	fclose(fp);
> +	name = strstr(bf, "Name:");
> +	tgids = strstr(bf, "Tgid:");
> +	ppids = strstr(bf, "PPid:");
> +
> +	if (name) {
> +		name += 5;  /* strlen("Name:") */
> +
> +		while (*name && isspace(*name))
> +			++name;
> +
> +		nl = strchr(name, '\n');
> +		if (nl)
> +			*nl = '\0';
> +
> +		size = strlen(name);
> +		if (size >= len)
> +			size = len - 1;
> +		memcpy(comm, name, size);
> +		comm[size] = '\0';
> +	} else
> +		pr_debug("Name: string not found for pid %d\n", pid);
> +
> +	if (tgids) {
> +		tgids += 5;  /* strlen("Tgid:") */
> +		while (*tgids && isspace(*tgids))
> +			++tgids;
> +
> +		nl = strchr(tgids, '\n');
> +		if (nl)
> +			*nl = '\0';
> +
> +		*tgid = atoi(tgids);
> +
> +	} else
> +		pr_debug("Tgid: string not found for pid %d\n", pid);
> +
> +	if (ppids) {
> +		ppids += 5;  /* strlen("PPid:") */
> +
> +		while (*ppids && isspace(*ppids))
> +			++ppids;
> +
> +		nl = strchr(ppids, '\n');
> +		if (nl)
> +			*nl = '\0';
> +
> +		*ppid = atoi(ppids);
> +	} else
> +		pr_debug("PPid: string not found for pid %d\n", pid);
>  
> -	return tgid;
> +	return 0;
>  }
>  
> -static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
> -					 struct machine *machine)
> +static int perf_event__prepare_comm(union perf_event *event, pid_t pid,
> +				    struct machine *machine,
> +				    pid_t *tgid, pid_t *ppid)
>  {
>  	size_t size;
> -	pid_t tgid;
> +
> +	*ppid = -1;
>  
>  	memset(&event->comm, 0, sizeof(event->comm));
>  
> -	if (machine__is_host(machine))
> -		tgid = perf_event__get_comm_tgid(pid, event->comm.comm,
> -						 sizeof(event->comm.comm));
> -	else
> -		tgid = machine->pid;
> +	if (machine__is_host(machine)) {
> +		if (perf_event__get_comm_ids(pid, event->comm.comm,
> +					     sizeof(event->comm.comm),
> +					     tgid, ppid) != 0) {
> +			return -1;
> +		}
> +	} else
> +		*tgid = machine->pid;
>  
> -	if (tgid < 0)
> -		goto out;
> +	if (*tgid < 0)
> +		return -1;
>  
> -	event->comm.pid = tgid;
> +	event->comm.pid = *tgid;
>  	event->comm.header.type = PERF_RECORD_COMM;
>  
>  	size = strlen(event->comm.comm) + 1;
> @@ -122,36 +167,35 @@ static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
>  				(sizeof(event->comm.comm) - size) +
>  				machine->id_hdr_size);
>  	event->comm.tid = pid;
> -out:
> -	return tgid;
> +
> +	return 0;
>  }
>  
> -static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
> -					 union perf_event *event, pid_t pid,
> -					 perf_event__handler_t process,
> -					 struct machine *machine)
> +static int perf_event__synthesize_comm(struct perf_tool *tool,
> +				       union perf_event *event, pid_t pid,
> +				       perf_event__handler_t process,
> +				       struct machine *machine,
> +				       pid_t *tgid, pid_t *ppid)
>  {
> -	pid_t tgid = perf_event__prepare_comm(event, pid, machine);
> -
> -	if (tgid == -1)
> -		goto out;
> +	if (perf_event__prepare_comm(event, pid, machine, tgid, ppid) != 0)
> +		return -1;
>  
>  	if (process(tool, event, &synth_sample, machine) != 0)
>  		return -1;
>  
> -out:
> -	return tgid;
> +	return 0;
>  }
>  
>  static int perf_event__synthesize_fork(struct perf_tool *tool,
> -				       union perf_event *event, pid_t pid,
> -				       pid_t tgid, perf_event__handler_t process,
> +				       union perf_event *event,
> +				       pid_t pid, pid_t tgid, pid_t ppid,
> +				       perf_event__handler_t process,
>  				       struct machine *machine)
>  {
>  	memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);
>  
> -	event->fork.ppid = tgid;
> -	event->fork.ptid = tgid;
> +	event->fork.ppid = ppid;
> +	event->fork.ptid = ppid;
>  	event->fork.pid  = tgid;
>  	event->fork.tid  = pid;
>  	event->fork.header.type = PERF_RECORD_FORK;
> @@ -343,14 +387,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
>  	char filename[PATH_MAX];
>  	DIR *tasks;
>  	struct dirent dirent, *next;
> -	pid_t tgid;
> +	pid_t tgid, ppid;
>  
>  	/* special case: only send one comm event using passed in pid */
>  	if (!full) {
> -		tgid = perf_event__synthesize_comm(tool, comm_event, pid,
> -						   process, machine);
> -
> -		if (tgid == -1)
> +		if (perf_event__synthesize_comm(tool, comm_event, pid,
> +						process, machine, &tgid, &ppid) != 0)
>  			return -1;
>  
>  		return perf_event__synthesize_mmap_events(tool, mmap_event, pid, tgid,
> @@ -378,12 +420,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
>  		if (*end)
>  			continue;
>  
> -		tgid = perf_event__prepare_comm(comm_event, _pid, machine);
> -		if (tgid == -1)
> +		if (perf_event__prepare_comm(comm_event, _pid, machine,
> +					     &tgid, &ppid) != 0)
>  			return -1;
>  
>  		if (perf_event__synthesize_fork(tool, fork_event, _pid, tgid,
> -						process, machine) < 0)
> +						ppid, process, machine) < 0)
>  			return -1;
>  		/*
>  		 * Send the prepared comm event
> -- 
> 2.1.0
>