Hi Hemant, As you know, you need to keep an eye on how (kprobes) event cache patchset from Masami settles down. For those who aren't CC'ed, please see the link below:
https://lkml.org/lkml/2014/10/31/207 On Sun, 02 Nov 2014 16:26:28 +0530, Hemant Kumar wrote: > This patch adds support to perf to record SDT events. When invoked, > the SDT event is looked up in the sdt-cache. If its found, an entry is > made silently to uprobe_events file and then recording is invoked, and > then the entry for the SDT event in uprobe_events is silently discarded. > > The SDT events are already stored in a cache file > (/var/cache/perf/perf-sdt-file.cache). > Although the file_hash table helps in addition or deletion of SDT events > from the cache, its not of much use when it comes to probing the actual > SDT event, because the key to this hash list is a file name and not the > SDT event name (which is given as an argument to perf record). So, we > won't be able to hash into it. It likely to be ended up with per-file or per-buildid cache files under ~/.debug directory. In this case we also need to have the (central) event-to-cache table anyway IMHO. > > To avoid this problem, we can create another hash list "event_hash" list > which will be maintained along with the file_hash list. > Whenever a user invokes 'perf record -e %provider:event, perf should > initialize the event_hash list and the file_hash list. > The key to event_hash list is calculated from the event name and its > provider name. Isn't it enough just to use provide name? I guess the provider names are (should be?) unique among a system although there's no absolute guarantee for that. > > event_hash sdt_note > |---------| ---------------- > | | | file_ptr |==> container file_sdt_ent > key = 129 =>| hlist ==|===|=> event_list=|==> to sdt notes hashed to > | | | name | same entry > |---------| | provider | > | | | note_list==|==> to other notes in the > key = 130 =>| hlist | --------------- same file > |---------| > > The entry at that key in event_hash contains a list of SDT notes hashed to > the same entry. It compares the name and provider to see if that is the SDT > note we are looking for. If yes, find out the file that contains this SDT > note. There is a file_ptr pointer embedded in this note which points to the > struct file_sdt_ent contained in the file_hash. From "file_sdt_ent" we will > find out the file name. > Convert this sdt note into a perf event and then write this into > uprobe_events file to be able to record the event. > Then, corresponding entries are added to uprobe_events file for > the SDT events. > After recording is done, these events are silently deleted from uprobe_events > file. The uprobe_events file is present in debugfs/tracing directory. > > To support the addition and deletion of SDT events to/from uprobe_events > file, a record_sdt struct is maintained which has the event data. > > An example usage: > > # perf record -e %libc:setjmp -aR sleep 10 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.277 MB perf.data (~12103 samples) ] > > # perf report --stdio > # To display the perf.data header info, please use --header/--header-only > # > # Samples: 1 of event 'libc:setjmp' > # Event count (approx.): 1 > # > # Overhead Command Shared Object Symbol > # ........ ....... ............. ............... > # > 100.00% sleep libc-2.16.so [.] __sigsetjmp > > > Signed-off-by: Hemant Kumar <hem...@linux.vnet.ibm.com> [SNIP] > +/* Session specific to SDT tracing */ > +struct record_sdt { > + bool sdt; /* is this SDT event tracing? */ > + char *str; /* hold the event name */ > +} rec_sdt; > + > +int trace_sdt_event(const char *str) > +{ > + int ret = 0; > + > + rec_sdt.sdt = true; > + rec_sdt.str = strdup(str); > + if (!rec_sdt.str) > + return -ENOMEM; > + ret = event_hash_list__lookup(str); > + return ret; > +} Hmm.. does it support multiple SDT events recorded in a session like: # perf record -e %libc:setjmp -e %libc:longjmp -aR sleep 10 ? [SNIP] > +/* Parse an SDT event */ > +static int parse_perf_sdt_event(struct perf_sdt_event *sev, > + struct perf_probe_event *pev) > +{ > + struct perf_probe_point *pp = &pev->point; > + > + pev->uprobes = true; > + pev->sdt = true; > + pev->event = strdup(sev->note->name); > + if (pev->event == NULL) > + return -ENOMEM; > + pev->group = strdup(sev->note->provider); > + if (pev->event == NULL) s/event/group/ > + return -ENOMEM; > + > + pp->file = strdup(sev->file_name); > + if (pp->file == NULL) > + return -ENOMEM; > + > + pp->function = strdup(sev->note->name); Missing NULL check. Also you need to free prior allocations in case of error. Thanks, Namhyung > + pp->offset = sev->note->addr.a64[0]; > + return 0; > +} -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
