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Message-ID: <55E115BD.6090909@huawei.com>
Date: Sat, 29 Aug 2015 10:15:25 +0800
From: "Wangnan (F)" <wangnan0@huawei.com>
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To: Alexei Starovoitov <ast@plumgrid.com>, <acme@redhat.com>
CC: <brendan.d.gregg@gmail.com>, <daniel@iogearbox.net>, <dsahern@gmail.com>,
        <hekuang@huawei.com>, <jolsa@kernel.org>, <xiakaixu@huawei.com>,
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        <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 32/32] bpf: Introduce function for outputing data to perf
 event
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On 2015/8/29 9:34, Alexei Starovoitov wrote:
> On 8/28/15 6:19 PM, Wangnan (F) wrote:
>> For me, I use bpf_output_trace_data() to output information like PMU 
>> count
>> value. Perf is the only receiver, so global collector is perfect. 
>> Could you
>> please describe your usecase in more detail?
>
> there is a special receiver in user space that only wants the data from
> the bpf program that it loaded. It shouldn't conflict with any other
> processes. Like when it's running, I still should be able to use perf
> for other performance analysis. There is no way to share single
> bpf:bpf_output_data event, since these user processes are completely
> independent.
>
I'd like to see whether it is possible to create dynamic tracepoints so
different receivers can listen on different tracepoints. For my side, maybe
I can encode format information into the new tracepoints so don't need
those LLVM patches.

For example:

# echo 'dynamic_tracepoint:mytracepoint <encode its format>' >> 
/sys/kernel/debug/tracing/dynamic_trace_events
# perf list
   ...
   dynamic_tracepoint:mytracepoint
   ...

In perf side we can encode the creation of dynamic tracepoint into 
bpf-loader
like what we currectly do for probing the kprobes.

This way reqires us to create a fresh new event source, in parallel with 
tracepoint. I'm not sure
how much work it needs. What do you think?

Thank you.

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