Subject: Re: [PATCH 32/32] bpf: Introduce function for outputing data to perf
 event
To: Wang Nan <wangnan0@huawei.com>, acme@redhat.com
References: <1440745570-150857-1-git-send-email-wangnan0@huawei.com>
 <1440745570-150857-33-git-send-email-wangnan0@huawei.com>
Cc: brendan.d.gregg@gmail.com, daniel@iogearbox.net, dsahern@gmail.com,
        hekuang@huawei.com, jolsa@kernel.org, xiakaixu@huawei.com,
        masami.hiramatsu.pt@hitachi.com, namhyung@kernel.org,
        a.p.zijlstra@chello.nl, lizefan@huawei.com, pi3orama@163.com,
        linux-kernel@vger.kernel.org,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Steven Rostedt <rostedt@goodmis.org>
From: Alexei Starovoitov <ast@plumgrid.com>
Message-ID: <55E10091.6020107@plumgrid.com>
Date: Fri, 28 Aug 2015 17:45:05 -0700
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0)
 Gecko/20100101 Thunderbird/38.2.0
MIME-Version: 1.0
In-Reply-To: <1440745570-150857-33-git-send-email-wangnan0@huawei.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1704
Lines: 42

On 8/28/15 12:06 AM, Wang Nan wrote:
> his patch adds a new trace event to establish infrastruction for bpf to
> output data to perf. Userspace perf tools can detect and use this event
> as using the existing tracepoint events.
>
> New bpf trace event entry in debugfs:
>
>       /sys/kernel/debug/tracing/events/bpf/bpf_output_data
>
> Userspace perf tools detect the new tracepoint event as:
>
>       bpf:bpf_output_data                          [Tracepoint event]
>
> Data in ring-buffer of perf events added to this event will be polled
> out, sample types and other attributes can be adjusted to those events
> directly without touching the original kprobe events.

Wang,
I have 2nd thoughts on this.
I've played with it, but global bpf:bpf_output_data event is limiting.
I'd like to use this bpf_output_trace_data() helper for tcp estats
gathering, but global collector will prevent other similar bpf programs
running in parallel.
So as a concept I think it's very useful, but we need a way to select
which ring-buffer to output data to.
proposal A:
Can we use ftrace:instances concept and make bpf_output_trace_data()
into that particular trace_pipe ?
proposal B:
bpf_perf_event_read() model is using nice concept of an array of
perf_events. Can we perf_event_open a 'new' event that can be mmaped
in user space and bpf_output_trace_data(idx, buf, buf_size) into it.
Where 'idx' will be an index of FD from perf_even_open of such
new event?

Thanks!

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/