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

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Date:   Thu, 10 Jan 2019 16:52:03 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Song Liu <songliubraving@...com>
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

Em Thu, Jan 10, 2019 at 07:30:22PM +0000, Song Liu escreveu:
> 
> 
> > 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

Thanks! I'm juggling a lot of stuff right now, so I didn't read all
patches in the series, just the first one and when I couldn't find where
perf_event_ksymbol() was being called in that patch nor by looking at
just the Subject for the others, I gave up and got back to pahole day :-)
 
> >> 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. 

With that 3/7 split I guess we can go on with what is in this patchset
if PeterZ is happy with it.

- Arnaldo