Messages in this thread | | | Date | Wed, 14 Apr 2021 15:08:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH] locking: Generic ticket-lock |
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On Wed, Apr 14, 2021 at 02:55:57PM +0200, Peter Zijlstra wrote: > On Wed, Apr 14, 2021 at 08:39:33PM +0800, Guo Ren wrote:
> > > + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence > > > + * uses atomic_fetch_add() which is SC to create an RCsc lock. > > This ^^^ then vvv > > > > +static __always_inline void ticket_lock(arch_spinlock_t *lock) > > > +{ > > > + u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > > atomic_fetch_add_acquire ? > > Then we must rely on the arch to implement RCsc atomics. And I for one > can never tell wth Risc-V actually does.
Anyway, if we can mandate that atomic acquire/release is RCsc, then yes we can do that but then we also need:
#define smp_mb__after_spinlock() smp_mb__after_atomic()
But currently atomic acquire/release is not RCsc (at the very least Power does RCtso -- and power gets to deal with any and all pain caused by that).
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