linux-kernel - Re: [PATCH 02/17] perf tools: Add evlist channel helpers

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Message-ID: <20160518132358.GB2370@redhat.com>
Date:	Wed, 18 May 2016 10:23:58 -0300
From:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, He Kuang <hekuang@...wei.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>, pi3orama@....com
Subject: Re: [PATCH 02/17] perf tools: Add evlist channel helpers

Em Wed, May 18, 2016 at 11:27:43AM +0800, Wangnan (F) escreveu:
> On 2016/5/13 21:05, Arnaldo Carvalho de Melo wrote:
> >Em Fri, May 13, 2016 at 07:55:59AM +0000, Wang Nan escreveu:
> >> Channels hold different groups of evsels which configured
> >> differently. It will be used for overwritable evsels, which allows
> >> perf

> >why not use multiple evlists? An "evlist" is a "list of evsels", why do
> >we need yet another way of grouping evlists?
 
> There's an assumption all over perf that there's only one evlist: in
> 'struct record' there's an 'evlist' pointer, in 'struct session'
> there's also an 'evlist' pointer.

Well, at some point there were none, and multiple tools used multiple
ways to deal with lists of events :-)

> Trying to change them to an array results in 181 errors, so I think
> fundamentally moving to multiple evlists is nearly impossible.

Well, in the next paragraph you give it some hope :-)
 
> Now I'm thinking introducing auxiliary evlists to perf record. We
> still obey one evlist assumption, only creates separated evlists for
> mmap.

Ok, that may be the way to go, i.e. linking evlists somehow for some
specific use cases, i.e. consuming events from multiple evlists,
probably sorting them via the ordered_events class, etc.

I have to review this more deeply to try and come with suggestions :-\

- Arnaldo