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Re: Re: [PATCH v4 5/5] perf/sdt: Add support to perf record to trace SDT events
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Hemant Kumar <hemant at linux dot vnet dot ibm dot com>
- Cc: Namhyung Kim <namhyung at kernel dot org>, linux-kernel at vger dot kernel dot org, srikar at linux dot vnet dot ibm dot com, peterz at infradead dot org, oleg at redhat dot com, hegdevasant at linux dot vnet dot ibm dot com, mingo at redhat dot com, anton at redhat dot com, systemtap at sourceware dot org, aravinda at linux dot vnet dot ibm dot com, penberg at iki dot fi, Arnaldo Carvalho de Melo <acme at redhat dot com>
- Date: Thu, 06 Nov 2014 23:56:22 +0900
- Subject: Re: Re: [PATCH v4 5/5] perf/sdt: Add support to perf record to trace SDT events
- Authentication-results: sourceware.org; auth=none
- References: <20141102105006 dot 21708 dot 28734 dot stgit at hemant-fedora> <20141102105557 dot 21708 dot 19032 dot stgit at hemant-fedora> <87lhnr5sbl dot fsf at sejong dot aot dot lge dot com> <54588905 dot 7040002 at linux dot vnet dot ibm dot com> <5458CD15 dot 4010101 at hitachi dot com> <874muew2hk dot fsf at sejong dot aot dot lge dot com> <5459E865 dot 6050207 at hitachi dot com> <545B1DDE dot 9000202 at linux dot vnet dot ibm dot com>
(2014/11/06 16:06), Hemant Kumar wrote:
> So, what should be our way forward here in case of SDT patchset wrt
> event_cache patchset? Shall we wait for event_cache patchset to be
> merged and then redesign the sdt_cache patchset according to new
> event_cache?
> Or, we can go ahead with the current sdt patchset (implementing the
> latest review comments) and we can change the sdt_cache according to the
> new event_cache design as and when required?
>
> What do you think?
Good question :)
In my opinion, we'd better consolidate sdt_cache to new cache subcommand
at first, since it is a user-visible change. If we consolidate it after
introducing sdt-cache, users will see that option is also banished.
And also, the cache-format may be a problem, since that involves a backward
compatibility issue. For now, I'm considering Namhyung's idea of merging
SDT and probe caches. If we can use SDT as a kind of probe cache, why do we
need to have both SDT cache and probe cache? SDT cache is currently have its
own format, but it also could be written as a probe format, as below.
In ~/.debug/probe/bu/ild-id:
%<PROVIDER>:<EVENT> _text+<OFFSET>
This lucks a semaphore location, but who cares? Anyway we can't change
the semaphore. We already have reader of this format and also this can
have arguments if you get it from sdt.note. :)
Moreover, we can share the cache file with perf-probe! :)
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com