linux-kernel - Re: [RFC PATCH tip 0/5] tracing filters with BPF

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Message-ID: <CAMEtUuyp0q9YSMq7OchEeWLz9oPYd3qQ+0SDV5Pt8F10KLbFpg@mail.gmail.com>
Date:	Thu, 5 Dec 2013 14:36:58 -0800
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Jovi Zhangwei <jovi.zhangwei@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH tip 0/5] tracing filters with BPF

On Thu, Dec 5, 2013 at 5:46 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> I know that it would be great to have the bpf filter run before
> recording of the tracepoint, but as that becomes quite awkward for a
> user interface, because it requires intimate knowledge of the kernel
> source, this speed up on the filter itself may be worth while to have
> it happen after the recording of the buffer. When it happens after the
> record, then the bpf has direct access to the event entry and its
> fields as described by the trace event format files.

I don't understand that 'awkward' part yet. What do you mean by 'knowledge of
the kernel'? By accessing pt_regs structure? Something else ?
Can we try fixing the interface first before compromising on performance?
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