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

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Date:   Wed, 10 Feb 2021 10:15:39 -0500
From:   Waiman Long <longman@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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 2/9/21 10:32 PM, Waiman Long wrote:
> On 2/2/21 1:57 PM, 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>
>> ---
>>   include/asm-generic/qrwlock.h | 24 ++++++++++++++++++------
>>   include/linux/rwlock.h        |  7 +++++++
>>   2 files changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/asm-generic/qrwlock.h 
>> b/include/asm-generic/qrwlock.h
>> index 84ce841ce735..0020d3b820a7 100644
>> --- a/include/asm-generic/qrwlock.h
>> +++ b/include/asm-generic/qrwlock.h
>> @@ -14,6 +14,7 @@
>>   #include <asm/processor.h>
>>     #include <asm-generic/qrwlock_types.h>
>> +#include <asm-generic/qspinlock.h>
>
> As said in another thread, qspinlock and qrwlock can be independently 
> enabled for an architecture. So we shouldn't include qspinlock.h here. 
> Instead, just include the regular linux/spinlock.h file to make sure 
> that arch_spin_is_locked() is available.

The csky architecture uses qrwlock but not qspinlock. So this patch can 
be problematic when compiling for csky.

Cheers,
Longman