Re: [PATCH] parisc: use per-pagetable spinlock

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Sat, 2019-04-06 at 15:36 -0400, Mikulas Patocka wrote:
> Parisc uses a global spinlock to protect pagetable updates in the TLB
> fault handlers. When multiple cores are taking TLB faults
> simultaneously, the cache line containing the spinlock becomes a
> bottleneck.

You can't do this.  As the comment in cache.c says: the lock is to
protect the merced bus, which runs between the CPUs on some systems. 
That means it must be a single, global lock.  Of course, on systems
without a merced bus, we don't need the lock at all, so runtime
patching might be usable to fix that case.

James