linux-kernel - Re: [LKP] [driver core] 570d020012: will-it-scale.per_thread

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Date:   Thu, 21 Feb 2019 21:40:30 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        kernel test robot <rong.a.chen@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, lkp@...org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [driver core] 570d020012: will-it-scale.per_thread_ops
 -12.2% regression

On Thu, Feb 21, 2019 at 10:12:17AM +0100, Greg Kroah-Hartman wrote:
>On Thu, Feb 21, 2019 at 04:39:27PM +0800, Wei Yang wrote:
>> >>> I don't think this is an issues of struct device.  As you said, struct
>> >>> device isn't access much during test.  Struct device may share slab page
>> >>> with some other data structures (signal related, or fd related (as in
>> >>> some other test cases)), so that the alignment of these data structures
>> >>> are affected, so caused the performance regression.
>> >>
>> >> But allocation of a structure should always be "properly" aligned, no
>> >> matter what something else did in the system as that is what kmalloc
>> >> ensures.  If not, then we have problems in our memory allocator :)
>> >>
>> >> So something is odd here, but I don't think that is it...
>> >
>> >If all these data structure are allocated with kmalloc() instead of
>> >kmem_cache_alloc(), then my guessing above seems incorrect ...
>> >
>> 
>> Seems we don't have special kmem_cache for device and device_private.
>
>Nor do we need one :)
>
>Remember, 'struct device' is included inside lots of other structures
>already, it is not very often created "on its own."
>

You are right, I get your point.

>thanks,
>
>greg k-h

-- 
Wei Yang
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