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Subject: Re: [OpenRISC] [PATCH v6 1/9] locking/qspinlock: Add
 ARCH_USE_QUEUED_SPINLOCKS_XCHG32
To:     Stafford Horne <shorne@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>
Cc:     guoren@kernel.org, linux-arch@vger.kernel.org,
        linux-xtensa@linux-xtensa.org, Guo Ren <guoren@linux.alibaba.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        linux-csky@vger.kernel.org, openrisc@lists.librecores.org,
        Anup Patel <anup@brainfault.org>, sparclinux@vger.kernel.org,
        linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org,
        Ingo Molnar <mingo@redhat.com>
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From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <1199af5f-275a-5812-fc73-f1d33449036b@redhat.com>
Date:   Thu, 8 Apr 2021 15:00:59 -0400
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On 4/6/21 7:52 PM, Stafford Horne wrote:
>
> For OpenRISC I did ack the patch to convert to
> CONFIG_ARCH_USE_QUEUED_SPINLOCKS_XCHG32=y.  But I think you are right, the
> generic code in xchg_tail and the xchg16 emulation code in produced by OpenRISC
> using xchg32 would produce very similar code.  I have not compared instructions,
> but it does seem like duplicate functionality.
>
> Why doesn't RISC-V add the xchg16 emulation code similar to OpenRISC?  For
> OpenRISC we added xchg16 and xchg8 emulation code to enable qspinlocks.  So
> one thought is with CONFIG_ARCH_USE_QUEUED_SPINLOCKS_XCHG32=y, can we remove our
> xchg16/xchg8 emulation code?

For the record, the latest qspinlock code doesn't use xchg8 anymore. It 
still need xchg16, though.

Cheers,
Longman