linux-kernel - Re: [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks

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Date:   Tue, 9 Feb 2021 14:25:19 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Waiman Long <longman@...hat.com>
Cc:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH v2 06/28] locking/rwlocks: Add contention detection for
 rwlocks

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@...hat.com>
> > > CC: Will Deacon <will@...nel.org>
> > > Acked-by: Peter Zijlstra <peterz@...radead.org>
> > > Acked-by: Davidlohr Bueso <dbueso@...e.de>
> > > Acked-by: Waiman Long <longman@...hat.com>
> > > Acked-by: Paolo Bonzini <pbonzini@...hat.com>
> > > Signed-off-by: Ben Gardon <bgardon@...gle.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

> Cheers,
> Longman
> 
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 0020d3b820a7..d7178a9439b5 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -10,11 +10,11 @@
>  #define __ASM_GENERIC_QRWLOCK_H
> 
>  #include <linux/atomic.h>
> +#include <linux/spinlock.h>
>  #include <asm/barrier.h>
>  #include <asm/processor.h>
> 
>  #include <asm-generic/qrwlock_types.h>
> -#include <asm-generic/qspinlock.h>
> 
>  /*
>   * Writer states & reader shift and bias.
> 
> 
>