linux-kernel - Re: [PATCH 2/2] clk: divider: improve the execution efficiency of determine

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Message-ID: <176144194442.3953.13998249458455926261@lazor>
Date: Sat, 25 Oct 2025 18:25:44 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@...nel.org>, Michael Turquette <mturquette@...libre.com>, chuan.liu@...ogic.com
Cc: linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, Chuan Liu <chuan.liu@...ogic.com>
Subject: Re: [PATCH 2/2] clk: divider: improve the execution efficiency of determine_rate()

Quoting Chuan Liu via B4 Relay (2025-10-21 03:12:31)
> From: Chuan Liu <chuan.liu@...ogic.com>
> 
> There is no need to evaluate further divider values once _is_best_div()
> finds one that matches the target rate.
> 
> Signed-off-by: Chuan Liu <chuan.liu@...ogic.com>
> ---
>  drivers/clk/clk-divider.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index 2601b6155afb..b92c4f800fa9 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -339,6 +339,9 @@ static int clk_divider_bestdiv(struct clk_hw *hw, struct clk_hw *parent,
>                         best = now;
>                         *best_parent_rate = parent_rate;
>                 }
> +
> +               if (best == rate)
> +                       break;

This needs a comment. I'm not even sure if it is correct either, because
the other exit from this loop happens if the parent rate can be
unchanged. I don't think we have any KUnit tests for this file, so
please add some tests that deal with this case explicitly (the parent
rate being unchanged as the desirable part).

A general comment: these patches have no benefit described in the commit
text. Do you see any performance improvement with this patch? I sorta
doubt this really matters because the number of dividers are typically
small. A single sentence commit text that only says there is no need
doesn't convince me that any work has been put in to research why the
code was written this way or even prove that making this change improves
anything.