Re: [PATCH 3/4] blktrace: add option to scale a trace

[Jens Axboe <axboe@kernel.dk>]

On 9/19/18 1:56 PM, Dennis Zhou wrote:
> On Wed, Sep 19, 2018 at 12:49:15PM -0600, Jens Axboe wrote:
>> On 9/19/18 12:25 PM, Dennis Zhou wrote:
>>> As we explore stacking traces, it is nice to be able to scale a trace to
>>> understand how the traces end up interacting.
>>>
>>> This patch adds scaling by letting the user pass in percentages to scale
>>> a trace by. When passed '--merge_blktrace_scalars="100", the trace is
>>> ran at 100% speed. If passed 50%, this will halve the trace timestamps.
>>> The new option takes in a comma separated list that index-wise pairs
>>> with the passed files in "--read_iolog".
>>
>> How is this different than replay_time_scale?
>>
> 
> I think merge_blktrace_scalars is a trace building parameter whereas
> replay_time scale is a runtime parameter. merge_blktrace_scalars is an
> index-paired list with the logs passed to --read_iolog allowing for each
> trace to be independently scaled. replay_time_scale happens at runtime
> and scales the entire trace uniformly. And because replay_time_scale
> happens at runtime, I'm not sure repurposing the numbers would be super
> intuitive.

Not sure I see the difference, if you just allow replay_time_scale to
take multiple values (one for each trace)?

-- 
Jens Axboe