linux-kernel - Re: [RFC] btf: Some structs are doubled because of struct ring

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Message-ID: <20191213183646.GB8994@krava>
Date:   Fri, 13 Dec 2019 19:36:46 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: Re: [RFC] btf: Some structs are doubled because of struct ring_buffer

On Fri, Dec 13, 2019 at 01:29:41PM -0500, Steven Rostedt wrote:
> On Fri, 13 Dec 2019 19:02:23 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Fri, Dec 13, 2019 at 12:11:18PM -0500, Steven Rostedt wrote:
> > > On Fri, 13 Dec 2019 08:51:57 -0800
> > > Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> > >   
> > > > It had two choices. Both valid. I don't know why gdb picked this one.
> > > > So yeah I think renaming 'ring_buffer' either in ftrace or in perf would be
> > > > good. I think renaming ftrace one would be better, since gdb picked perf one
> > > > for whatever reason.  
> > > 
> > > Because of the sort algorithm. But from a technical perspective, the
> > > ring buffer that ftrace uses is generic, where the perf ring buffer can
> > > only be used for perf. Call it "event_ring_buffer" or whatever, but
> > > it's not generic and should not have a generic name.  
> > 
> > Your ring buffer was so generic that I gave up trying to use it after
> > trying for days :-( (the fundamental problem was that it was impossible
> > to have a single cpu buffer; afaik that is still true today)
> 
> Yeah, but that could have been fixed, and the only reason it's not
> today, is because it requires more overhead to do so.
> 
> IIRC, the main reason that you didn't use it then, is because it wasn't
> fully lockless at the time (it is today), and you couldn't use it from
> NMI context.
> 
> > 
> > Nor is the perf buffer fundamentally specific to perf, but there not
> > being another user means there has been very little effort to remove
> > perf specific things from it.
> 
> I took a look at doing so, and it was not a trivial task.
> 
> > 
> > There are major design differences between them, which is
> > unquestionably, but I don't think it is fair to say one is more or less
> > generic.
> > 
> > How about we rename both? I'm a bit adverse to long names, so how about
> > we rename the perf one to perf_buffer and the trace one to trace_buffer?
> 
> I'm fine with this idea! Now what do we call the ring buffer that
> tracing uses, as it is not specific for tracing, it was optimized for
> splicing. But sure, I can rename it to trace_buffer. I just finished
> renaming perf's...
> 
> Thinking about this, perhaps we should remove the word "ring" from
> both. That is:
> 
>   perf_buffer and trace_buffer ?

sounds good to me.. and too good to be true ;-)
please let me know if I should send the perf change

thanks,
jirka