Re: [PATCH RFC 4/5] block: add a statistic table for io latency

[Guoqing Jiang <guoqing.jiang@cloud.ionos.com>]

Hi Ming,

On 7/8/20 4:06 PM, Guoqing Jiang wrote:
> On 7/8/20 4:02 PM, Guoqing Jiang wrote:
>>> Hi Guoqing,
>>>
>>> I believe it isn't hard to write a ebpf based script(bcc or 
>>> bpftrace) to
>>> collect this kind of performance data, so looks not necessary to do it
>>> in kernel.
>>
>> Hi Ming,
>>
>> Sorry, I don't know well about bcc or bpftrace, but I assume they 
>> need to
>> read the latency value from somewhere inside kernel. Could you point
>> how can I get the latency value? Thanks in advance!
>
> Hmm, I suppose biolatency is suitable for track latency, will look 
> into it.

I think biolatency can't trace data if it is not running, also seems no 
place
inside kernel have recorded such information for ebpf to read, correct me
if my understanding is wrong.

And as cloud provider,we would like to know data when necessary instead
of collect data by keep script running because it is expensive than just 
read
node IMHO.

Thanks,
Guoqing