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Message-ID: <37978ed1-5f28-40c1-8396-24f4aa6a7a23@quicinc.com>
Date: Thu, 27 Jun 2024 23:13:14 +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 10:35 PM, Greg KH wrote:
> On Thu, Jun 27, 2024 at 10:29:43PM +0800, quic_zijuhu wrote:
>> 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.
>
> But do we really know that ahead of time? If so, how, just by virtue of
> this being the first field? If so, then no, keep the container_of.
>
yes. the 2nd parameter for match() must be devr->data by below reasons:
1) devres.c only call match() by this way match(dev, dr->data, match_data).
2) all implements of match() don't do such redundant operations to get
dr->data. such as devm_action_match()/devm_pages_match()/....
3) API user should only know address devr->data and known nothing about
devres internal struct devres. so they should not write their match() by
involving the struct.
for below match() type definition, the 1st parameter @dev have already
have fixed meaning.
typedef int (*dr_match_t)(struct device *dev, void *res, void *match_data);
suppose your 3rd question have typo error.
>> 2) compare with right data type
>> original type of @p is void __percpu * returned by
>> __devm_alloc_percpu().
>
> It's pointer math, no need for types, right?
>
yes, it is more simpler for no need for types.
but it think it is more normative to compare with user original types as
this change do.
>> @data is storing a pointer type void __percpu * as shown by below
>> statement within __devm_alloc_percpu().
>> *(void __percpu **)p = pcpu;
>
> Again, it's not very obvious so you better document the heck out of it
> in your changelog text.
>
okay, will add comments after code review done.
> thanks,
>
> greg k-h
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