linux-kernel - Re: [PATCH v2 00/15] tracing: 'hist' triggers

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Date:	Mon, 2 Mar 2015 14:31:57 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH v2 00/15] tracing: 'hist' triggers

On Mon, 2 Mar 2015 11:14:54 -0800
Alexei Starovoitov <ast@...mgrid.com> wrote:
 
> I think we both want to see in-kernel aggregation.
> This 'hist' stuff is trying to do counting and even map sorting
> in the kernel, whereas with bpf programs I'm moving
> all of these decisions to user space.
> I understand your desire to avoid any user level scripts
> and do everything via 'cat' and debugfs, but imo that's
> very limiting. I think it's better to do slim user space
> scripting language that can translate to bpf even in
> embedded setups. Then users will be able to aggregate
> whatever they like, whereas with 'hist' approach
> they're limited to simple counters.
> trace_events_trigger.c - 1466 lines - that's quite a bit
> of code that will be rarely used. Kinda goes counter
> to embedded argument. Why add this to kernel
> when bpf programs can do the same on demand?

At Collab, a lot of people came to me telling me they love the debugfs
system. Because it's everywhere they go. You remove that, you remove
most users (including myself).


> Also the arguments about stable ABI apply as well.
> The format of 'hist' file would need to be stable, so will
> be hard to extend it. With bpf programs doing aggregation
> the kernel ABI exposure is much smaller.

I disagree with this statement.

> So would you consider working together on adding
> clean bpf+tracepoints infra and corresponding
> user space bits?
> We can have small user space parser/compiler for
> 'hist:keys=common_pid.execname,id.syscall:vals=hitcount'
> strings that will convert it into bpf program and you'll
> be able to use it in embedded setups ?

Make sure it also works on android.

-- Steve
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