Messages in this thread |  | | Date | Wed, 22 Oct 2014 13:50:22 +0530 | From | Hemant Kumar <> | Subject | Re: [PATCH v3 5/5] perf/sdt: Add support to perf record to trace SDT events |
| |
Hi Masami,
On 10/22/2014 12:15 PM, Masami Hiramatsu wrote: > Hi Hemant, > > (2014/10/10 19:59), Hemant Kumar wrote: >> The SDT events are already stored in a cache file >> (/var/cache/perf/perf-sdt-file.cache). > Please describe what this patch does at first. >
Sure, will do that.
>> 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. >> >> 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. >> >> 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. > OK, I have some comments on this. > >> An example usage: >> >> # ./perf record -e %user_app:fun_start -aR /home/user_app > At first, I'd like to add SDT support for adding probes too, like below; > > ./perf probe -a '%user_app:fun_start $vars'
But I think, previously we discussed that we won't be having "perf probe" for SDT events. We list them and probe/trace them using "perf record" directly.
> So, maybe we don't need to remove the SDT-based events silently, nor > hide it from users. I think you just need to add new sdt events and > verify it if there is. > > BTW, for silently adding event, I'll introduce --quite(-q) option for > perf probe. So you'll just need to set silent flag with that. > > > Thank you, > >
-- Thanks, Hemant Kumar
|  |