linux-kernel - Re: [PATCH RFC/RFT v2 1/8] drivers: base: support cpu cache information interface to userspace via sysfs

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Date:	Mon, 17 Feb 2014 18:26:15 +0000
From:	Sudeep Holla <Sudeep.Holla@....com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Sudeep Holla <Sudeep.Holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh@...nel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH RFC/RFT v2 1/8] drivers: base: support cpu cache information
 interface to userspace via sysfs

Hi Greg,

On 13/02/14 15:55, Sudeep Holla wrote:
> Hi Greg,
> 
> On 11/02/14 00:13, Greg Kroah-Hartman wrote:
>> On Mon, Feb 10, 2014 at 06:09:58PM +0000, Sudeep Holla wrote:
>>> On 07/02/14 19:29, Greg Kroah-Hartman wrote:
>>>> On Fri, Feb 07, 2014 at 04:49:16PM +0000, Sudeep Holla wrote:
>>>>> From: Sudeep Holla <sudeep.holla@....com>
>>>>>
>>>>> This patch adds initial support for providing processor cache information
>>>>> to userspace through sysfs interface. This is based on already existing
>>>>> implementations(x86, ia64, s390 and powerpc) and hence the interface is
>>>>> intended to be fully compatible.
>>>>>
>>>>> The main purpose of this generic support is to avoid further code
>>>>> duplication to support new architectures and also to unify all the existing
>>>>> different implementations.
>>>>>
>>>>> This implementation maintains the hierarchy of cache objects which reflects
>>>>> the system's cache topology. Cache objects are instantiated as needed as
>>>>> CPUs come online. The cache objects are replicated per-cpu even if they are
>>>>> shared. A per-cpu array of cache information maintained is used mainly for
>>>>> sysfs-related book keeping.
>>>>
>>>> I thought I asked that you not use "raw" kobjects for this, instead
>>>> using 'struct device' or just an attribute group?
>>>>
>>>
>>> Correct, sorry I should have mentioned here instead of cover letter that it's
>>> not yet done. Since the changes involved other architectures, I posted v2 to get
>>> early feedback and testing. More over it's one place to fix now instead of 4
>>> unlike before.
>>
>> Ok, I'll wait to review it after you do the device conversion.
>>
>>> Just adding cache as a device as you suggested won't suffice here. As we need to
>>> track multiple cache indices for each cpu, devices are needed for each cache
>>> index. I tried using device_create_with_groups which provides all we need in one
>>> api for cache indices but since cpu devices are not associated with any class,
>>> it fails if class is NULL. Any suggestions ?
>>
>> Make the cpu devices be part of a class?
> 
> I was able to convert these to use struct device instead of raw kobjects. But it
> requires some changes in order to retain the existing sysfs path mainly due to
> the fact that cpus are using legacy subsys_system_register and introducing
> cpu_class conflicts with cpu bus. The base changes in the driver core is as
> below. Is this acceptable ? or any other alternate suggestions ?
>

Any feedback on this ? If this is acceptable I can post my changes converting
raw kobjects to devices attributes along with this change in a separate patch.

Regards,
Sudeep


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