linux-kernel - Re: [PATCH] driver core: auxiliary bus: Optimize auxiliary_match

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Message-ID: <20250902124923.GG10073@unreal>
Date: Tue, 2 Sep 2025 15:49:23 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dave Ertman <david.m.ertman@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org,
	Zijun Hu <zijun.hu@....qualcomm.com>
Subject: Re: [PATCH] driver core: auxiliary bus: Optimize auxiliary_match_id()

On Tue, Sep 02, 2025 at 08:42:24PM +0800, Zijun Hu wrote:
> On 2025/9/2 20:20, Greg Kroah-Hartman wrote:
> > On Tue, Sep 02, 2025 at 08:05:32PM +0800, Zijun Hu wrote:
> >> From: Zijun Hu <zijun.hu@....qualcomm.com>
> >>
> >> Variable @match_size is fixed in auxiliary_match_id().
> >>
> >> Optimize the function by moving the logic calculating the variable
> >> out of the for loop.
> > Optimize it how?  Does this actually result in a difference somehow, if
> > so, what?
> > 
> 
> auxiliary_match_id() repeatedly calculates variable @match_size in the
> for loop. however, the variable is fixed actually. so it is enough to
> calculate the variable once.
> 
> Optimize it by moving the logic calculating the variable out of the for
> loop, and it result in:
> 
> 1) calculate the variable once instead of repeatedly.
> 2) it will return as early as possible if device name is unexpected,
> namely, (@p == NULL).
> 
> so this fix will improve performance.

While the proposed change is valid, it is not a fix and unlikely give
any performance benefits too. First, smart compilers should optimize this
code and perform single calculation instead in the loop and second the
result will be in cache anyway.

Thanks

> 
> > Please be specific.
> 
> will give more commit message in v2.
> 
> thanks