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SubjectRe: [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks
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On 2/9/21 7:27 PM, Waiman Long wrote:
> On 2/9/21 5:25 PM, Guenter Roeck wrote:
>> On Tue, Feb 09, 2021 at 04:46:02PM -0500, Waiman Long wrote:
>>> On 2/9/21 3:39 PM, Guenter Roeck wrote:
>>>> On Tue, Feb 02, 2021 at 10:57:12AM -0800, Ben Gardon wrote:
>>>>> rwlocks do not currently have any facility to detect contention
>>>>> like spinlocks do. In order to allow users of rwlocks to better
>>>>> manage
>>>>> latency, add contention detection for queued rwlocks.
>>>>>
>>>>> CC: Ingo Molnar <mingo@redhat.com>
>>>>> CC: Will Deacon <will@kernel.org>
>>>>> Acked-by: Peter Zijlstra <peterz@infradead.org>
>>>>> Acked-by: Davidlohr Bueso <dbueso@suse.de>
>>>>> Acked-by: Waiman Long <longman@redhat.com>
>>>>> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
>>>>> Signed-off-by: Ben Gardon <bgardon@google.com>
>>>> When building mips:defconfig, this patch results in:
>>>>
>>>> Error log:
>>>> In file included from include/linux/spinlock.h:90,
>>>>                    from include/linux/ipc.h:5,
>>>>                    from include/uapi/linux/sem.h:5,
>>>>                    from include/linux/sem.h:5,
>>>>                    from include/linux/compat.h:14,
>>>>                    from arch/mips/kernel/asm-offsets.c:12:
>>>> arch/mips/include/asm/spinlock.h:17:28: error: redefinition of
>>>> 'queued_spin_unlock'
>>>>      17 | #define queued_spin_unlock queued_spin_unlock
>>>>         |                            ^~~~~~~~~~~~~~~~~~
>>>> arch/mips/include/asm/spinlock.h:22:20: note: in expansion of macro
>>>> 'queued_spin_unlock'
>>>>      22 | static inline void queued_spin_unlock(struct qspinlock
>>>> *lock)
>>>>         |                    ^~~~~~~~~~~~~~~~~~
>>>> In file included from include/asm-generic/qrwlock.h:17,
>>>>                    from ./arch/mips/include/generated/asm/qrwlock.h:1,
>>>>                    from arch/mips/include/asm/spinlock.h:13,
>>>>                    from include/linux/spinlock.h:90,
>>>>                    from include/linux/ipc.h:5,
>>>>                    from include/uapi/linux/sem.h:5,
>>>>                    from include/linux/sem.h:5,
>>>>                    from include/linux/compat.h:14,
>>>>                    from arch/mips/kernel/asm-offsets.c:12:
>>>> include/asm-generic/qspinlock.h:94:29: note: previous definition of
>>>> 'queued_spin_unlock' was here
>>>>      94 | static __always_inline void queued_spin_unlock(struct
>>>> qspinlock *lock)
>>>>         |                             ^~~~~~~~~~~~~~~~~~
>>> I think the compile error is caused by the improper header file
>>> inclusion
>>> ordering. Can you try the following change to see if it can fix the
>>> compile
>>> error?
>>>
>> That results in:
>>
>> In file included from ./arch/mips/include/generated/asm/qrwlock.h:1,
>>                   from ./arch/mips/include/asm/spinlock.h:13,
>>                   from ./include/linux/spinlock.h:90,
>>                   from ./include/linux/ipc.h:5,
>>                   from ./include/uapi/linux/sem.h:5,
>>                   from ./include/linux/sem.h:5,
>>                   from ./include/linux/compat.h:14,
>>                   from arch/mips/kernel/asm-offsets.c:12:
>> ./include/asm-generic/qrwlock.h: In function
>> 'queued_rwlock_is_contended':
>> ./include/asm-generic/qrwlock.h:127:9: error: implicit declaration of
>> function 'arch_spin_is_locked'
>>
>> Guenter
>
> It is because in arch/mips/include/asm/spinlock.h, asm/qrwlock.h is
> included before asm/qspinlock.h. The compilation error should be gone
> if the asm/qrwlock.h is removed or moved after asm/qspinlock.h.

After thinking a bit more, I think we should remove asm/qrwlock.h in
arch/mips/include/asm/spinlock.h. qrwlock and qspinlocks are
independent. An architecture can include one but not the other. Also
there is no point in including qrwlock.h in a asm/spinlock.h.

Regards,
Longman

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