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

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Date:	Tue, 11 Nov 2014 11:10:30 -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 Tue, Nov 11, 2014 at 03:53:42PM +0900, Masami Hiramatsu escreveu:
> (2014/11/10 21:23), Arnaldo Carvalho de Melo wrote:
> > Em Mon, Nov 10, 2014 at 07:59:24PM +0900, Masami Hiramatsu escreveu:
> >> 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>
 
> Yes, for the elf and sdt cache, we don't need --probe.
> Note that "[]" means optional. If we would like to add some probe cache,
> we need a spec of probe definition.

I understand that, its just that it looked superfluous at that specific
place, where you are explaining how to add ELF 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?

> This is only for adding the probe cache (not elf, nor sdt), which requires
> a probe definition. Moreover, I'd like to unify the specification of the
> probe definition with perf-probe. In that case, --probe is more natural.

What I meant was, what is wrong with replacing:

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

With:

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

And have it figure out that what is being added is a probe and do the
right thing?
 
> >> 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?
> 
> In most cases, it may be OK, but it is also possible to cause unexpected
> result when mis-typing. I think if <FILE> is always starting at '/', it
> is easy to identify.

We can keep the explicit switch (--probe-del) perhaps to resolve
ambiguities, if they happen, but make it so that it is not strictly
required for the common case.
 
- Thanks,

- Arnaldo
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