linux-kernel - Re: [PATCH v6 perf, bpf-next 1/7] perf, bpf: Introduce PERF_RECORD

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Message-ID: <CCB26BF8-9FF5-4BBF-84BE-878CF0D3882A@fb.com>
Date:   Thu, 10 Jan 2019 19:30:22 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     lkml <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v6 perf, bpf-next 1/7] perf, bpf: Introduce
 PERF_RECORD_KSYMBOL



> On Jan 10, 2019, at 10:55 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> Em Thu, Jan 10, 2019 at 06:40:37PM +0000, Song Liu escreveu:
>> 
>> 
>>> On Jan 10, 2019, at 10:24 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>>> 
>>> Em Wed, Jan 09, 2019 at 11:21:05AM -0800, Song Liu escreveu:
>>>> 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 couldn't find where this gets used, the intention here is just to
>>> add the interfaces and afterwards is that you will wire this up? I would
>>> like to test the whole shebang to see it working.
>> 
>> I guess you meant PERF_RECORD_BPF_EVENT not being used? 
>> 
>> PERF_RECORD_KSYMBOL is used by BPF in 3/7 and 5/7. I tested 
> 
> Oops, I didn't look at 3/7, just read its cset summary line and as it
> says:
> 
> Subject: [PATCH v6 perf, bpf-next 3/7] perf, bpf: introduce PERF_RECORD_BPF_EVENT
> 
> I didn't thought it was related, perhaps break it down into one that
> states that it is wiring up PERF_RECORD_KSYMBOL, and at that point we
> could just test it, getting the notifications for new kallsyms related
> to BPF?

Good idea! I will split it into two patches as:

[3/8] perf, bpf: generate PERF_RECORD_KSYMBOL for BPF program 
[4/8] perf, bpf: introduce PERF_RECORD_BPF_EVENT

> 
>> PERF_RECORD_BPF_EVENT with dump_trace. As we separate RECORD_KSYMBOL from
>> RECORD_BPF_EVENT, user space won't use BPF_EVENT until annotation support.  
> 
> Right, so why not just introduce PERF_RECORD_KSYMBOL, make it be used by
> tooling, etc, then move on to PERF_RECORD_BPF_EVENT?

I'd like to make sure we all agree on the new ABI for RECORD_KSYMBOL and 
RECORD_BPF_EVENT. Multiple user space tools dependent on RECORD_BPF_EVENT,
for example, bcc and auditing. Finalizing RECORD_BPF_EVENT will unblock the 
development of these tools. On perf side, it will take us quite some time 
to finish annotation. Ideally, I don't want to block the development of 
other tools for so long. 

Thanks,
Song