Re: [RFC PATCH v13 2/4] blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary

[bot+bpf-ci]

> blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary

TL;DR: Commit message only: it restates the code comment instead of giving the
motivation (monitoring without drgn) for the new iocost_ioc_tick tracepoint.
Not a bug.

> blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary
>
> Add iocost_ioc_tick, emitted once per period from ioc_timer_fn() with
> the overall controller state: period_us, vrate, busy_level, active iocg
> count and usage percentage.  busy_level, cur_period, nr_active and
> usage_us_sum are complete at the emission point.  usage is wall time
> over wall time, summed over iocgs, and is not capped at 100.  vrate and
> period_us reflect the current controller state, which an io.cost.qos
> write may have changed mid-period.
>
> The event fires every period the controller is running, including
> steady states, plus one final tick before the controller goes idle, so
> the transition to dormancy is directly visible.  The active iocg count
> is only gathered when the tracepoint is enabled.
>
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>

this isn't a bug, but the middle of the first paragraph ("busy_level,
cur_period, nr_active and usage_us_sum are complete at the emission point
... which an io.cost.qos write may have changed mid-period") restates the
block comment added above the tracepoint call in ioc_timer_fn() almost word
for word.

The reason for adding the event only appears in the comment in
include/trace/events/iocost.h ("so basic monitoring doesn't require drgn").

Could the changelog say why a per-period summary event is needed, for
example the monitoring-without-drgn motivation, rather than repeating the
code comment?


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