Messages in this thread |  | | Date | Wed, 22 Oct 2014 15:45:38 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v3 5/5] perf/sdt: Add support to perf record to trace SDT events |
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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.
> 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'
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,
-- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com
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