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

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Date:	Tue, 7 Jul 2015 10:43:15 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	pi3orama <pi3orama@....com>
CC:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
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	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf record: Allow passing perf's own pid to '--filter'



On 2015/7/6 23:40, Arnaldo Carvalho de Melo wrote:
> 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 :-)

But what about user want to use real shell variables also?

  perf record -e raw_syscalls:* "common_pid !="'$PERF_PID'" && 
common_pid != $X_PID"

Or

  perf record -e raw_syscalls:* "common_pid !=\$PERF_PID && common_pid 
!= $X_PID"

right?

However, since you and Steven prefer '$' than '@' and '@' has its own 
meaning 'at' in 'perf probe', I'll use '$' in my next version.

I looked your new code. You added perf_evsel__append_filter() to enable 
us append a filter expression in '(%s) <op> (%s)' manner, and also 
perf_evlist__set_filter_pid() to add 'common_pid != %d' expression. They 
are nice scaffolds if we'd like to add a new cmdline option 
'--filter-pids' and '--filter-perf'. However, I think we should let 
users who use --filter take full control of their filters, instead of 
providing many helpers which can do similar things to confuse them. So I 
decide not to use those functions you added these days in my next version.

Thank you.

>
> - Arnaldo


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