linux-kernel - Re: [PATCH 2/5] vdso: Add comment about reason for vdso struct ordering

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Date: Mon, 1 Jul 2024 17:17:59 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] vdso: Add comment about reason for vdso struct
 ordering



On 01/07/2024 16:31, Anna-Maria Behnsen wrote:
> Vincenzo Frascino <vincenzo.frascino@....com> writes:
> 
>> On 01/07/2024 15:47, Anna-Maria Behnsen wrote:
>>> Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
>>
>> nit: Can you please add something in the commit message?
> 
> Sure, I would propose the following:
> 
> The struct vdso_data is optimized for fast access to the often required
> struct members. The optimization is not documented in the struct
> description but it should be kept in mind, when working with the
> vdso_data struct.
> 
> Add a comment to the struct description.
> 
>>
>> Otherwise:
>>
>> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
> 
> Thanks!
>

Works for me. Thanks!

>>> ---
>>>  include/vdso/datapage.h | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
>>> index d04d394db064..7647e0946f50 100644
>>> --- a/include/vdso/datapage.h
>>> +++ b/include/vdso/datapage.h
>>> @@ -77,6 +77,10 @@ struct vdso_timestamp {
>>>   * vdso_data will be accessed by 64 bit and compat code at the same time
>>>   * so we should be careful before modifying this structure.
>>>   *
>>> + * The ordering of the struct members is optimized to have fast access to the
>>> + * often required struct members which are related to CLOCK_REALTIME and
>>> + * CLOCK_MONOTONIC. This information is stored in the first cache lines.
>>> + *
>>>   * @basetime is used to store the base time for the system wide time getter
>>>   * VVAR page.
>>>   *
>>>

-- 
Regards,
Vincenzo