Re: [PATCH 0/9] introduce the log_issue_time option

[Damien Le Moal <dlemoal@kernel.org>]

On 8/29/24 02:06, Jens Axboe wrote:
> On 8/27/24 1:08 AM, Shin'ichiro Kawasaki wrote:
>> When write_lat_log option is set, fio outputs the 'clat' completion
>> latency log file. This clat log can be used to analyze IO latency. This
>> file can also be considered as an IO trace file as each IO entry can
>> fully describe an IO when the --log_offset and --log_prio options are
>> also used. However, using the clat log file as an IO trace is inaccurate
>> because the time field of each entry uses millisecond units, which is
>> too coarse for fast IOs (e.g. when using SSDs). This series proposes the
>> new option 'log_issue_time' to address the inaccuracy problem. When this
>> option is set, fio adds another field to the log file entries to log an
>> IO issuing time in nanoseconds.
>>
>> The first four patches in the series clean up the current code as
>> preparation. The 5th patch introduces the 'log_issue_time' option. The
>> following two patches document the new option. The last two patches add
>> two test cases to check the log file format.
> 
> In general this looks fine, and I think it's a useful feature. However,
> should we have an option to make the generic time in the log entry be
> in nsec as well?

I am not sure if it is that useful given that the entry time field does not
directly correspond to any I/O time. But to be consistent with the other time
fields, I may be good to add this option. That is easy to do.

-- 
Damien Le Moal
Western Digital Research