Re: [RFC PATCH v6 3/5] blk-iocost: add iocost_ioc_tick tracepoint for per-period device summary

[Tao Cui <cui.tao@linux.dev>]

Hello, Tejun.

在 2026/9/22 03:37, Tejun Heo 写道:
> Hello, Tao.
> 
> On Fri, 18 Sep 2026 13:49:59 +0800, Tao Cui wrote:
> 
>> +	/*
>> +	 * vrate and period_us change right below; snapshot the values
>> +	 * this period ran in so the tick below reports the period's own
>> +	 * parameters instead of the next period's.
>> +	 */
>> +	tick_period_us = ioc->period_us;
>> +	tick_vrate = ioc->vtime_base_rate;
> 
> Everything the tick reports is already final at this point. busy_level
> was just computed, running and cur_period haven't changed yet, and
> nr_active and usage_us_sum are complete. Can you emit the tracepoint here
> instead and drop the snapshots? The event can then read the fields
> directly and the only cost outside the static key is the nr_active
> increment.
> 

That's a cleaner placement.  The tracepoint is now emitted
before the period refresh, after busy_level is clamped, and the
temporary tick_* snapshots are removed; the event reads the ioc fields
directly.  nr_active remains the only cost outside the static key.

Thanks,
Tao

> Looks fine otherwise.
> 
> Thanks.
> 
> --
> tejun