On Wed, Apr 07, 2021 at 11:47:49AM +0200, Peter Zijlstra wrote: > On Wed, Apr 07, 2021 at 08:52:08AM +0900, Stafford Horne wrote: > > 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? > > CONFIG_ARCH_USE_QUEUED_SPINLOCKS_XCHG32 is guaranteed crap. > > All the architectures that have wanted it are RISC style LL/SC archs, > and for them a cmpxchg loop is a daft thing to do, since it reduces the > chance of it behaving sanely. > > Why would we provide something that's known to be suboptimal? If an > architecture chooses to not care about determinism and or fwd progress, > then that's their choice. But not one, I feel, we should encourage. Thanks, this is the response I was hoping my comment would provoke. So not enabling CONFIG_ARCH_USE_QUEUED_SPINLOCKS_XCHG32 for architectures unless they really want it should be the way. -Stafford
