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

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Date:	Sat, 08 Nov 2014 13:38:39 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	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

(2014/11/07 23:43), Namhyung Kim wrote:
> Hi Masami,
> 
> 2014-11-07 (금), 17:21 +0900, Masami Hiramatsu:
>> Hello,
>>
>> Here, I've tried to describe my idea of perf-cache subcommand interface.
>> It is just a design review, not implemented yet :)
>> Please give me your comments/ideas!
>>
>> Command-line Synopsis
>> =====================
>>
>> Current "perf buildid-cache [options]" are directly mapped to
>> "perf cache --buildid [options]".
>>
>> And adding --sdt for managing SDT caches as below.
>>
>>   Add or update SDT events in <FILES>
>>     perf cache --sdt --add|--update <FILES>
>>
>>   Remove all SDT events for <FILES>
>>     perf cache --sdt --remove <FILES>
>>
>>   List all SDT events
>>     perf cache --sdt --list
>>
>> And --probes for managing probe-caches as below.
>>
>>   Add new probe-cache entries for kernel, <PATH> or <MOD>.
>>     perf cache --probe [--exec <PATH>|--module <MOD>] --add <SPEC>
>>
>>   Delete existing probe-cache entries for kernel, <PATH> or/and <BUILDID>.
>>     perf cache --probe --del [<GROUP>:]<EVENT>[@<PATH>][#<BUILDID>]
>>
>>   Or remove all entires for given FILES
>>     perf cache --probe --remove <FILES>
>>
>>   List the probe caches(including SDT) for kernel, <PATH>, or/and <BUILDID>.
>>     perf cache --probe --list [@<PATH>][#<BUILDID>]
>>
>>   Query the probe definitions.
>>     perf cache --probe --query [<GROUP>:]<EVENT>[@<PATH>][#<BUILDID>]
>>
>> Note that --probes also can be used for managing SDT events, which has % prefix
>> e.g.
>>   Add all SDT events for <PATH>
>>     perf cache --probe --exec <PATH> --add '%*:*'
>>
>>   Remove some SDT events for <PATH>
>>     perf cache --probe --del '%some:events@<PATH>'
>>
>>   Or remove all SDT events for <BUILDID>
>>     perf cache --probe --del '%*:*#<BUILDID>'
> 
> I'd prefer sub-command to option for this mandatory (and exclusive)
> behavior.  What about like this?

I consider this will also confusing users because it's different from
other subcommands. And Arnaldo gives us a better solution :)

> 
>   perf cache kprobe add [-m <module>] <spec> [<spec>...]
>   perf cache kprobe del [<group>:]<event> [<event>...]
>   perf cache kprobe list [-m <module>]
> 
>   perf cache uprobe add -x <path> <spec> [<spec>...]
>   perf cache uprobe del [<group>:]<event> [<event>...]
>   perf cache uprobe list [-x <path>]

Since perf has only "probe" subcommand, we shouldn't separate
uprobe and kprobe.

> 
>   perf cache sdt [add|del|update] <file> [<file>...]
>   perf cache sdt list [-b <build-id>] [<file>...]
> 
> 
>>
>>
>> File Format
>> ===========
>> All the cache files are placed under ~/.debug/ by default.
>> The paths of buildid cache of binary/symbols are not changed.
>>
>> The SDT/probe caches are placed under the ~/.debug/.probes/path/to/bin/bu/ildid
>> and that is linked to ~/.debug/.probes/.buildid/bu/ildid
>> # To avoid conflict with files under /probes/*, I picked up .probes/.
> 
> However, to be used with perf record, we need a way to find a matching
> probe cache file from a event name (or group/provider name, preferably).
> What about having something like below:
> 
>   $ cat ~/.debug/.probes/event.map
>   PROVIDER1 /path/to/some/where
>   PROVIDER2 /path/to/other/place

Hmm, agreed. We'd better have this kind of provider index file to
accelerate searching.

> When perf record see a cached event used, it first searches its
> provider/group name from the event.map file.  And then read bulid-id
> from the matching file on the path and finally find a cached event
> definition from ~/.debug/.probes/.buildid/bu/ildid file.
> 
> 
>>
>> This SDT/probe caches contain probe-definitions as following format.
>> ----
>> #buildid:BUILDID
>> #path:PATH
>> p:%PROVIDER/EVENT PATH:OFFSET [ARGS]
> 
> It seems PATH is redundant and we don't need to repeat it everyline
> IMHO.  Since it need post-processing anyway, maybe it's better to just
> make it simpler, like:
> 
>   %:PROVIDER/EVENT OFFSET [ARGS]

Hmm, this is not good because this line will not be able to pass to
tracing/uprobe_events...
And also, I think we can compress this cache with gzip, then such
redundancy will not be a problem.

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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