linux-kernel - Re: [PATCH RFC v4 net-next 00/26] BPF syscall, maps, verifier, samples, llvm

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Message-ID: <CAE40pdcsEnCg-zVyYR-hkYZ9Zd4kmX2BS11cFWAKZK3=HfBUMg@mail.gmail.com>
Date:	Thu, 14 Aug 2014 12:17:39 -0700
From:	Brendan Gregg <brendan.d.gregg@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v4 net-next 00/26] BPF syscall, maps, verifier,
 samples, llvm

On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <ast@...mgrid.com> wrote:
[...]
> Tracing use case got some improvements as well. Now eBPF programs can be
> attached to tracepoint, syscall, kprobe and C examples are more usable:
> ex1_kern.c - demonstrate how programs can walk in-kernel data structures
> ex2_kern.c - in-kernel event accounting and user space histograms
> See patch #25

This is great, thanks! I've been using this new support, and
successfully ported an an older tool of mine (bitesize) to eBPF. I was
using the block:block_rq_issue tracepoint, and performing a custom
in-kernel histogram, like in the ex2_kern.c example, for I/O size.

I also did some quick overhead testing and found eBPF with JIT to be
relatively fast. (I'd share numbers but it's platform specific.) The
syscall tracepoints were a bit slower than hoped, for what I think is
a well known issue.

Are there thoughts in general for how this might be used for embedded
devices, where installing clang/llvm might be prohibitive? Compile on
another system and move the binaries over? thanks,

Brendan
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