linux-kernel - Re: [RFC] perf-cache command interface design

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Date:	Mon, 10 Nov 2014 10:23:21 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>,
	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, oleg@...hat.com,
	hegdevasant@...ux.vnet.ibm.com, mingo@...hat.com,
	systemtap@...rceware.org, aravinda@...ux.vnet.ibm.com,
	penberg@....fi, brendan.d.gregg@...il.com,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: [RFC] perf-cache command interface design

Em Mon, Nov 10, 2014 at 07:59:24PM +0900, Masami Hiramatsu escreveu:
> Hello,
> 
> Here is the second try for the probe-cache. This version simplifies
> the synopsis, and unifies the SDT and probe caches.
> Please give me your comments/ideas!
> 
> Command-line Synopsis
> =====================
> 
> Add elf(or symbols) and probe-caches of SDT if exists in <FILES>
>  perf cache --add <FILES> [--probe <SPEC>] # for user programs

Why the --probe above? Shouldn't this be just (if you are talking about
ELF files only):

perf cache --add <FILES>
 
>  perf cache --kcore <FILE> [--probe <SPEC>] # for kcore ?

Adrian, aren't kcore files easily identifiable as such and thus could be
added as:

 perf cache --add <FILES>
 
>  perf cache --probe <SPEC>  # for the current kernel

Why do we need a --probe here? Don't they always start with a character
that is seldomly used in ELF file names and thus we could get away with
not requiring --probe?
 
> Remove caches related to <FILES> or <BUILDIDS>
>  perf cache --remove <FILES>|<BUILDIDS>
> 
> Show all probe caches(including SDT) or buildids
>  perf cache --list [probe|buildid]
> 
> Delete existing probe-cache entries for kernel, <PATH> or/and <BUILDID>.
>  perf cache　--probe-del [<GROUP>:]<EVENT>[@<PATH>][#<BUILDID>]

Ditto, i.e. can't we just use:

 perf cache　--remove [<GROUP>:]<EVENT>[@<PATH>][#<BUILDID>]

And it figure out that this is a probe that is being removed?

> Query the probe definitions.
>  perf cache --query [<GROUP>:]<EVENT>[@<PATH>][#<BUILDID>]

Replace --query with --show?
 
> File Format
> ===========
> All the cache files are placed under ~/.debug/ by default.
> Elf caches are ~/.debug/path/to/file/bu/ildid/elf
> Symbols caches are ~/.debug/path/to/file/bu/ildid/syms
> Probes(and SDT) are ~/.debug/path/to/file/bu/ildid/probes
> And ~/.debug/path/to/file/bu/ildid/ is linked to ~/.debug/.buildid/bu/ildid
> Optionally, we can gzip the probes file.

Ok!
 
> This probe caches contain probe-definitions as following format.
> ----
> #buildid:BUILDID
> #spec:SDT
> p:sdt_<PROVIDER>/<EVENT> PATH:OFFSET [ARGS]
> ...
> #spec:* $params
> p:probe_<GROUP>/<EVENT> _text+OFFSET [ARGS]
> ...
> ----
> So the #spec: line gives the information what probe spec has been given.
> This will be used for updating.
> 
> And all the "probe_" and "sdt_" prefix will be replaced by % in the command line,
> e.g.
> 
>  perf record -e %<PROVIDER>/<EVENT> -> this records sdt_PROVIDER/EVENT
> 
> Thank you,
> 
> -- 
> Masami HIRAMATSU
> Software Platform Research Dept. Linux Technology Research Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu.pt@...achi.com
> 
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