Re: [OpenRISC] [PATCH v6 1/9] locking/qspinlock: Add ARCH_USE_QUEUED_SPINLOCKS_XCHG32

[Waiman Long]

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