netdev - Re: [PATCH perf,bpf 0/5] reveal invisible bpf programs

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Message-ID: <71189F83-A09F-4A03-95EC-694D37FD7675@fb.com>
Date:   Thu, 22 Nov 2018 18:13:32 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "acme@...nel.org" <acme@...nel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH perf,bpf 0/5] reveal invisible bpf programs

Hi Peter,

> On Nov 22, 2018, at 1:32 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, Nov 21, 2018 at 11:54:57AM -0800, Song Liu wrote:
>> Changes RFC -> PATCH v1:
>> 
>> 1. In perf-record, poll vip events in a separate thread;
>> 2. Add tag to bpf prog name;
>> 3. Small refactorings.
>> 
>> Original cover letter (with minor revisions):
>> 
>> This is to follow up Alexei's early effort to show bpf programs
>> 
>>   https://urldefense.proofpoint.com/v2/url?u=https-3A__www.spinics.net_lists_netdev_msg524232.html&d=DwIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=dR8692q0_uaizy0jkrBJQM5k2hfm4CiFxYT8KaysFrg&m=3--n8O2EZfFY2WyGCKt0u4zd73778zD7xmoNHi9tMCU&s=3DY93pysLN-m1tgYmd7YAyQGNSq6KpYKucIJcB3nofc&e=
>> 
>> In this version, PERF_RECORD_BPF_EVENT is introduced to send real time BPF
>> load/unload events to user space. In user space, perf-record is modified
>> to listen to these events (through a dedicated ring buffer) and generate
>> detailed information about the program (struct bpf_prog_info_event). Then,
>> perf-report translates these events into proper symbols.
>> 
>> With this set, perf-report will show bpf program as:
>> 
>>   18.49%     0.16%  test  [kernel.vmlinux]    [k] ksys_write
>>   18.01%     0.47%  test  [kernel.vmlinux]    [k] vfs_write
>>   17.02%     0.40%  test  bpf_prog            [k] bpf_prog_07367f7ba80df72b_
>>   16.97%     0.10%  test  [kernel.vmlinux]    [k] __vfs_write
>>   16.86%     0.12%  test  [kernel.vmlinux]    [k] comm_write
>>   16.67%     0.39%  test  [kernel.vmlinux]    [k] bpf_probe_read
>> 
>> Note that, the program name is still work in progress, it will be cleaner
>> with function types in BTF.
>> 
>> Please share your comments on this.
> 
> So I see:
> 
>  kernel/bpf/core.c:void bpf_prog_kallsyms_add(struct bpf_prog *fp)
> 
> which should already provide basic symbol information for extant eBPF
> programs, right?

Right, if the BPF program is still loaded when perf-report runs, symbols 
are available. 

> And (AFAIK) perf uses /proc/kcore for annotate on the current running
> kernel (if not, it really should, given alternatives, jump_labels and
> all other other self-modifying code).
> 
> So this fancy new stuff is only for the case where your profile spans
> eBPF load/unload events (which should be relatively rare in the normal
> case, right), or when you want source annotated asm output (I normally
> don't bother with that).

This patch set adds two pieces of information:
1. At the beginning of perf-record, save info of existing BPF programs;
2. Gather information of BPF programs load/unload during perf-record. 

(1) is all in user space. It is necessary to show symbols of BPF program
that are unloaded _after_ perf-record. (2) needs PERF_RECORD_BPF_EVENT 
from the ring buffer. It covers BPF program loaded during perf-record 
(perf record -- bpf_test). 


> That is; I would really like this fancy stuff to be an optional extra
> that is typically not needed.
> 
> Does that make sense?

(1) above is always enabled with this set. I added option no-bpf-events 
to disable (2). I guess you prefer the (2) is disabled by default, and 
enabled with an option?

Thanks,
Song