linux-kernel - Re: [PATCH] devres: Simple code optimization

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Date: Thu, 27 Jun 2024 22:29:43 +0800
From: quic_zijuhu <quic_zijuhu@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <rafael@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devres: Simple code optimization

On 6/27/2024 9:54 PM, Greg KH wrote:
> On Thu, Jun 27, 2024 at 09:47:16PM +0800, Zijun Hu wrote:
>> Initialize an uninitialized struct member for devres_open_group()
>> and simplify devm_percpu_match() implementation.
> 
> Huge hint, when you say "and" or "also" in a patch, it's a good idea to
> split it up into different commits, right?
> 
you are right.
i would like to split this change into two changes within a patchset
even if this change is *very* simple.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>> This change is intend to replace below one:
>> https://lore.kernel.org/lkml/1718629765-32720-1-git-send-email-quic_zijuhu@quicinc.com/#t
> 
> Why?  SHouldn't this be v2 instead?
> 
this change has different title and maybe be identified as different
patch, so i send it as v1.
>>  drivers/base/devres.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
>> index 3df0025d12aa..5b1d498e83ab 100644
>> --- a/drivers/base/devres.c
>> +++ b/drivers/base/devres.c
>> @@ -567,6 +567,7 @@ void * devres_open_group(struct device *dev, void *id, gfp_t gfp)
>>  	grp->id = grp;
>>  	if (id)
>>  		grp->id = id;
>> +	grp->color = 0;
>>  
>>  	spin_lock_irqsave(&dev->devres_lock, flags);
>>  	add_dr(dev, &grp->node[0]);
>> @@ -1172,9 +1173,9 @@ static void devm_percpu_release(struct device *dev, void *pdata)
>>  
>>  static int devm_percpu_match(struct device *dev, void *data, void *p)
>>  {
>> -	struct devres *devr = container_of(data, struct devres, data);
>> +	void __percpu *ptr = *(void __percpu **)data;
>>  
>> -	return *(void **)devr->data == p;
>> +	return ptr == (void __percpu *)p;
> 
> What exactly is being "optimized" here?
> 
1) remove redundant container_of() and devr->data operations
   pointer parameter @data already is address of devr->data.
2) compare with right data type
    original type of @p is void __percpu * returned by
__devm_alloc_percpu().

@data is storing a pointer type void __percpu * as shown by below
statement within __devm_alloc_percpu().
*(void __percpu **)p = pcpu;

> And where did the container_of go?  You just lost all type-safeness.
> 
see above comments 1) and 2).
> thanks,
> 
> greg k-h