Re: [PATCH v2 bpf-next] bpf: sharing bpf runtime stats with /dev/bpf_stats

[Song Liu <songliubraving@fb.com>]

> On Mar 17, 2020, at 12:54 PM, Song Liu <songliubraving@fb.com> wrote:
> 
> 
> 
>> On Mar 17, 2020, at 12:30 PM, Daniel Borkmann <daniel@iogearbox.net> wrote:
>> 
>> On 3/16/20 9:33 PM, Song Liu wrote:
>>> Currently, sysctl kernel.bpf_stats_enabled controls BPF runtime stats.
>>> Typical userspace tools use kernel.bpf_stats_enabled as follows:
>>>  1. Enable kernel.bpf_stats_enabled;
>>>  2. Check program run_time_ns;
>>>  3. Sleep for the monitoring period;
>>>  4. Check program run_time_ns again, calculate the difference;
>>>  5. Disable kernel.bpf_stats_enabled.
>>> The problem with this approach is that only one userspace tool can toggle
>>> this sysctl. If multiple tools toggle the sysctl at the same time, the
>>> measurement may be inaccurate.
>>> To fix this problem while keep backward compatibility, introduce a new
>>> bpf command BPF_ENABLE_RUNTIME_STATS. On success, this command enables
>>> run_time_ns stats and returns a valid fd.
>>> With BPF_ENABLE_RUNTIME_STATS, user space tool would have the following
>>> flow:
>>>  1. Get a fd with BPF_ENABLE_RUNTIME_STATS, and make sure it is valid;
>>>  2. Check program run_time_ns;
>>>  3. Sleep for the monitoring period;
>>>  4. Check program run_time_ns again, calculate the difference;
>>>  5. Close the fd.
>>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> 
>> Hmm, I see no relation to /dev/bpf_stats anymore, yet the subject still talks
>> about it?
> 
> My fault. Will fix..
> 
>> 
>> Also, should this have bpftool integration now that we have `bpftool prog profile`
>> support? Would be nice to then fetch the related stats via bpf_prog_info, so users
>> can consume this in an easy way.
> 
> We can add "run_time_ns" as a metric to "bpftool prog profile". But the 
> mechanism is not the same though. Let me think about this. 

Btw, I plan to add this in separate set. Please let me know if it 
preferable to have them in the same set. 

Thanks,
Song