linux-kernel - Re: [PATCH] perf record: Allow passing perf's own pid to '--filter'

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Message-ID: <20150706154035.GI16826@kernel.org>
Date:	Mon, 6 Jul 2015 12:40:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	pi3orama <pi3orama@....com>
Cc:	Wang Nan <wangnan0@...wei.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"kan.liang@...el.com" <kan.liang@...el.com>,
	"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"cody@...ux.vnet.ibm.com" <cody@...ux.vnet.ibm.com>,
	"jacob.w.shin@...il.com" <jacob.w.shin@...il.com>,
	"standby24x7@...il.com" <standby24x7@...il.com>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
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	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf record: Allow passing perf's own pid to '--filter'

Em Mon, Jul 06, 2015 at 11:00:10PM +0800, pi3orama escreveu:
> 发自我的 iPhone
 
> > 在 2015年7月6日，下午9:56，Arnaldo Carvalho de Melo <acme@...nel.org> 写道：
> > I.e. having something in the filter expression that gets transformed
> > into the tools' pid, I have no problem with that, just curious about
> > what would be the best character to signal that a substitution needs to
> > be performed, if it is really '@...', as my first selection would be
> > '$VAR',
 
> $ has special meaning for shell. Using $ in cmdline require users use escaping or '' quoted string. Therefore I believe @ should be better. What do you think?

Yeah, that gets in the way, as it gets in the way for '!', i.e.
negating, and even tho, that is what is used in strace (and in 'perf
trace'):

  strace -e \!open,write ls

Or:

  strace -e '!open,write' ls

But apart from that, it would be good if expressions used in 'perf
probe' and here could have as much as possible the same semantics for
those markers, i.e. 'perf probe' already uses @ for some stuff, probably
the meaning is for "at", i.e. something at some place.

'$' strongly associated with variables, so I don't think it would be a
big problem to enclose expressions where variables (we may end having
others, no?)  in '', i.e.

  perf record -e sched:*switch --filter 'common_pid != $PERF_PID' -a

Doesn't look so ugly or cumbersome :-)

- Arnaldo
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