Date:	Thu, 30 Apr 2015 21:37:04 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Wang Nan <wangnan0@...wei.com>, davem@...emloft.net,
	acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	masami.hiramatsu.pt@...achi.com, jolsa@...nel.org
CC:	lizefan@...nel.org, linux-kernel@...r.kernel.org, pi3orama@....com,
	hekuang@...wei.com, bgregg@...flix.com
Subject: Re: [RFC PATCH 00/22] perf tools: introduce 'perf bpf' command to
 load eBPF programs.

On 4/30/15 3:52 AM, Wang Nan wrote:
> This series of patches is an approach to integrate eBPF with perf.
> After applying these patches, users are allowed to use following
> command to load eBPF program compiled by LLVM into kernel:
>
>   $ perf bpf sample_bpf.o
>
> The required BPF code and the loading procedure is similar to Alexei
> Starovoitov's libbpf in sample/bpf, with following exceptions:
>
>   1. The section name are not required leading with 'kprobe/' or
>      'kretprobe/'. Without such leading, any valid C var name can be use.
>
>   2. A 'config' section can be provided to describe the position and
>      arguments of a program. Syntax is identical to 'perf probe'.
>
> An example is pasted at the bottom of this cover letter. In that
> example, mybpfprog is configured by string in config section, and will
> be probed at __alloc_pages_nodemask. sample_bpf.o is generated using:
>
>   $ $CLANG -I/usr/src/kernel/include -I/usr/src/kernel/usr/include -D__KERNEL__ \
> 	 -Wno-unused-value -Wno-pointer-sign \
> 	 -O2 -emit-llvm -c sample_bpf.c -o -| $LLC -march=bpf -filetype=obj -o \
> 	 sample_bpf.o
>
> And can be loaded using:
>
>   $ perf bpf sample_bpf.o
>
> This series is only a limited functional. Following works are on the
> todo list:
>
>   1. Unprobe kprobe stubs used by eBPF programs when unloading;
>
>   2. Enable eBPF programs to access local variables and arguments
>      by utilizing debuginfo;
>
>   3. Output data in perf way.
>
> In this series:
>
> Patch 1/22 is a bugfix in perf probe, and may be triggered by following
> patches;
>
> Patch 2-3/22 are preparation, add required macros and syscall
> definition into perf source tree.
>
> Patch 4/22 add 'perf bpf' command.
>
> Patch 5-20/22 are labor works, which parse the ELF object file, collect
> information in object files, create maps needed by programs, link map
> and programs, config programs and load programs into kernel.
>
> Patch 21-22/22 are the final work. Patch 21 creates kprobe points which
> will be used by eBPF programs, patch 22 creates perf file descriptors
> then attach eBPF programs on them.

I'm very happy to see this work. Looks great. All patches are 
impressively clean and concise.
I think patches 1-3 are ready to go into Arnaldo's perf tree right now.
4 and above are clean and polished, but probably need to go into
some 'staging area' like a branch of perf tree, since I suspect the
user interface may change a little in the coming months and it's
a bit too early to expose 'perf bpf' command to every perf user ?
Arnaldo, Ingo, what do you guys think should be the arrangement?
'perf/bpf' branch in acme/linux.git or in tip/tip.git ?

I have few comments for patches 18 and 19, but let's figure out
the long term plan first.

We're also working in parallel on creating a new tracing language
that together with llvm backend can be used as a single shared library
that can be called from perf or anything else.
Then clang compilation step will be gone and programs can be run
as 'perf bpf file.bpf'.

Thanks!

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