Re: [RFC PATCH] blk-iocost: Optimize the ioc_refreash_vrate() function

[Tejun Heo]

On Sun, Nov 29, 2020 at 10:37:18AM +0800, Baolin Wang wrote:
> The ioc_refreash_vrate() will only be called in ioc_timer_fn() after
> starting a new period or stopping the period.
> 
> So when starting a new period, the variable 'pleft' in ioc_refreash_vrate()
> is always the period's time, which means if the abs(ioc->vtime_err)
> is less than the period's time, the vcomp is 0, and we do not need
> compensate the vtime_rate in this case, just set it as the base vrate
> and return.
> 
> When stopping the period, the ioc->vtime_err will be cleared to 0,
> and we also do not need to compensate the vtime_rate, just set it as
> the base vrate and return.

Before, the function did something which is conceptually discrete and
describable. After, its operation is intertwined with when it's called. I
don't think this sort of micro optimizations are beneficial in cold paths.

Thanks.

-- 
tejun