Re: [PATCH perf/core v4 14/19] perf buildid-cache: Scan and import user SDT events to probe cache

[Hemant Kumar]

On 04/26/2016 02:34 PM, Masami Hiramatsu wrote:
> From: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
>
> perf buildid-cache --add <binary> scans given binary and add
> the SDT events to probe cache. "sdt_" prefix is appended for
> all SDT providers to avoid event-name clash with other pre-defined
> events. It is possible to use the cached SDT events as other cached
> events, via perf probe --add "sdt_<provider>:<event>=<event>".
>
> e.g.
>    ----
>    # perf buildid-cache --add /lib/libc-2.17.so
>    # perf probe --cache --list | head -n 5
>    /usr/lib/libc-2.17.so (a6fb821bdf53660eb2c29f778757aef294d3d392):
>    sdt_libc:setjmp=setjmp
>    sdt_libc:longjmp=longjmp
>    sdt_libc:longjmp_target=longjmp_target
>    sdt_libc:memory_heap_new=memory_heap_new
>    # perf probe -x /usr/lib/libc-2.17.so \
>      -a sdt_libc:memory_heap_new=memory_heap_new
>    Added new event:
>      sdt_libc:memory_heap_new (on memory_heap_new
>     in /usr/lib/libc-2.17.so)
>
>    You can now use it in all perf tools, such as:
>
>            perf record -e sdt_libc:memory_heap_new -aR sleep 1
>
>    # perf probe -l
>      sdt_libc:memory_heap_new (on new_heap+183 in /usr/lib/libc-2.17.so)
>    ----

Patch looks good to me. Have a few questions below :

What about the same binary path having different build-ids. For e.g
a binary say, "test" has some markers, we add it to the cache. And,
then the file gets rebuilt again with different build-id now. And we try
to add to the cache again. It shows multiple entries in the cache :
# perf probe --cache --list
/home/hemant/test (157380727e2b3854395aa915dfc91dbccc02058b):
sdt_user_test:marker1=marker1
/home/hemant/test (64c0a018636e6d5145b09fc65839c1a4a7899f18):
sdt_user_test:marker1=marker1
/home/hemant/test (c9e34759ae95b68fa385831041c5d9e0dd1697fb):
sdt_user_test:marker1=marker1
...

But, perf list sdt shows only one entry (which it should) :
# perf list sdt

List of pre-defined events (to be used in -e):

  sdt_user_test:marker1                                [SDT event]

perf probe also works as expected :
# perf probe -x /home/hemant/test %sdt_user_test:marker1
Added new event:
  sdt_user_test:marker1  (on %marker1 in /home/hemant/test)

You can now use it in all perf tools, such as:

    perf record -e sdt_user_test:marker1 -aR sleep 1

So, the question is, do we delete the previous entries for "test" from
the cache once we get a newer version of "test"?

> Note that SDT event entries in probe-cache file is somewhat different
> from normal cached events. Normal one starts with "#", but SDTs are
> starting with "%".
>
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
[SNIP]
> +	list_for_each_entry(note, &sdtlist, note_list) {
> +		ret = snprintf(sdtgrp, 64, "sdt_%s", note->provider);
> +		if (ret < 0)
> +			break;
> +		/* Try to find same-name entry */
> +		entry = probe_cache__find_by_name(pcache, sdtgrp, note->name);

Wouldn't it be better to compare the build-id rather than the event
name? So, if there is a new sdt event added to a binary, its build-id will
change. And, if there is no change, the build-id remains the same.

Only if there is a change in the build-id, we can go for searching the
event name. This two level check can help optimizing the search.

> +		if (!entry) {
> +			entry = probe_cache_entry__new(NULL);
> +			if (!entry) {
> +				ret = -ENOMEM;
> +				break;
> +			}
> +			entry->sdt = true;
> +			ret = asprintf(&entry->spev, "%s:%s=%s", sdtgrp,
> +					note->name, note->name);
> +			if (ret < 0)
> +				break;
> +			entry->pev.event = strdup(note->name);
> +			entry->pev.group = strdup(sdtgrp);
> +			list_add_tail(&entry->list, &pcache->list);
> +		}
> +		ret = asprintf(&buf, "p:%s/%s %s:0x%llx",
> +				sdtgrp, note->name, pathname,
> +				sdt_note__get_addr(note));
> +		if (ret < 0)
> +			break;
> +		strlist__add(entry->tevlist, buf);
> +		free(buf);
> +		entry = NULL;
> +	}
> +	if (entry)
> +		probe_cache_entry__delete(entry);
> +	cleanup_sdt_note_list(&sdtlist);
> +	return ret;
> +}
> +
>   static int probe_cache_entry__write(struct probe_cache_entry *entry, int fd)
>   {
>   	struct str_node *snode;
>   	struct iovec iov[3];
> +	const char *prefix = entry->sdt ? "%" : "#";
>   	int ret;
>
> -	pr_debug("Writing cache: #%s\n", entry->spev);
> -	iov[0].iov_base = (void *)"#"; iov[0].iov_len = 1;
> +	pr_debug("Writing cache: %s%s\n", prefix, entry->spev);
> +	iov[0].iov_base = (void *)prefix; iov[0].iov_len = 1;
>   	iov[1].iov_base = entry->spev; iov[1].iov_len = strlen(entry->spev);
>   	iov[2].iov_base = (void *)"\n"; iov[2].iov_len = 1;
>   	ret = writev(fd, iov, 3);
> diff --git a/tools/perf/util/probe-file.h b/tools/perf/util/probe-file.h
> index ba7b6d3..55322f1 100644
> --- a/tools/perf/util/probe-file.h
> +++ b/tools/perf/util/probe-file.h
> @@ -21,6 +21,7 @@ int probe_file__del_strlist(int fd, struct strlist *namelist);
>   /* Cache of probe definitions */
>   struct probe_cache_entry {
>   	struct list_head	list;
> +	bool			sdt;
>   	struct perf_probe_event pev;
>   	char			*spev;
>   	struct strlist		*tevlist;
> @@ -35,6 +36,7 @@ struct probe_cache *probe_cache__new(const char *target);
>   int probe_cache__add_entry(struct probe_cache *pcache,
>   			   struct perf_probe_event *pev,
>   			   struct probe_trace_event *tevs, int ntevs);
> +int probe_cache__scan_sdt(struct probe_cache *pcache, const char *pathname);
>   int probe_cache__commit(struct probe_cache *pcache);
>   void probe_cache__delete(struct probe_cache *pcache);
>   int probe_cache__remove_entries(struct probe_cache *pcache,

--
Thanks,
Hemant Kumar