Re: [PATCH] trace2: log progress time and throughput

> 
> 
> On 5/12/20 5:44 PM, Emily Shaffer wrote:
>> Rather than teaching only one operation, like 'git fetch', how to write
>> down throughput to traces, we can learn about a wide range of user
>> operations that may seem slow by adding tooling to the progress library
>> itself. Operations which display progress are likely to be slow-running
>> and the kind of thing we want to monitor for performance anyways. By
>> showing object counts and data transfer size, we should be able to
>> make some derived measurements to ensure operations are scaling the way
>> we expect.
>>
>> Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
> 
> We need to be careful here.  The region_enter and _leave calls need
> to always be properly nested.  Having an implicit region within the
> progress code means the code path between all of the different start_ 
> and stop_progress calls need to not interleave with explicit regions.
> 
> How about putting something like this in stop_progress:
> 
>      struct json_writer jw = JSON_WRITER_INIT;
>      jw_object_begin(&jw, 0);
>      jw_object_intmax(&jw, "total", p->total);
>      if (p->throughput)
>          jw_object_intmax(&jw, "throughput", p->throughput->curr_total);
>      /*
>       * and so on...
>       * and maybe include the elapsed time in since the start_progress.
>       */
>      jw_end(&jw);
>      trace2_data_json("progress", NULL, p->title, &jw);
>      jw_release(&jw);
> 
> That will give you a single record summary of the progress meter
> and you won't have to worry about any interleaving.
> 
> You could also add a bit to `struct progress` to let you opt-in
> or opt-out of the message on a case-by-case basis.
> 
> Jeff