Re: [PATCH v10 perf, bpf-next 1/9] perf, bpf: Introduce PERF_RECORD_KSYMBOL

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Song Liu <songliubraving@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, Netdev <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>, David Ahern <dsahern@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v10 perf, bpf-next 1/9] perf, bpf: Introduce PERF_RECORD_KSYMBOL
Date: Thu, 17 Jan 2019 11:58:54 -0300	[thread overview]
Message-ID: <20190117145854.GD5823@kernel.org> (raw)
In-Reply-To: <A411D89E-0B62-4DE7-9D70-CD57672FD20A@fb.com>

Em Thu, Jan 17, 2019 at 02:49:10PM +0000, Song Liu escreveu:
> 
> 
> > On Jan 17, 2019, at 4:56 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > On Wed, Jan 16, 2019 at 08:29:23AM -0800, Song Liu wrote:
> >> For better performance analysis of dynamically JITed and loaded kernel
> >> functions, such as BPF programs, this patch introduces
> >> PERF_RECORD_KSYMBOL, a new perf_event_type that exposes kernel symbol
> >> register/unregister information to user space.
> >> 
> >> The following data structure is used for PERF_RECORD_KSYMBOL.
> >> 
> >>    /*
> >>     * struct {
> >>     *      struct perf_event_header        header;
> >>     *      u64                             addr;
> >>     *      u32                             len;
> >>     *      u16                             ksym_type;
> >>     *      u16                             flags;
> >>     *      char                            name[];
> >>     *      struct sample_id                sample_id;
> >>     * };
> >>     */
> > 
> > So I've cobbled together the attached patches to see how it would work
> > out..
> > 
> > I didn't convert ftrace trampolines; because ftrace code has this
> > uncanny ability to make my head hurt. But I don't think it should be
> > hard, once one figures out the right structure to stick that
> > kallsym_node thing in (ftrace_ops ?!).
> > 
> > It is compiled only, so no testing what so ever (also, no changelogs).
> > 
> > I didn't wire up the KSYM_TYPE thing; I'm wondering if we really need
> > that, OTOH it really doesn't hurt having it either.
> > 
> > One weird thing I noticed, wth does bpf_prog_kallsyms_add() check
> > CAP_ADMIN ?! Surely even a non-priv JIT'ed program generates symbols,
> > why hide those?
> > 
> > Anyway; with the one nit about the get_names() thing sorted:
> > 
> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > 
> > (thanks for sticking with this)
> > <peterz-latch-next.patch><peterz-kallsym.patch><peterz-kallsym-bpf.patch>
> 
> Aha, now I get the point on perf_event_ksymbol(). Yeah this approach is 
> definitely better. 
> 
> While I run more tests with these patches, could we get current in 
> perf/core? This will enable the development of user space tools like
> bcc. 
> 
> Also, I current base this set on bpf-next tree, as tip/perf/core is 
> 4 week old. Shall I rebase the set on Linus' tree? Or shall I wait for
> tip/perf/core?

So, can you post one last set, this time with PeterZ's Acked-by,
assuming you're sorting out the get_names() thing, and I can try merging
this into my perf/core branch, then pushing it out to Ingo, my perf/core
starts from tip/perf/urgent, so should be new enough.

I'd then right after testing it send a pull request to Ingo, synching
everything.

- Arnaldo