Re: [rfc] "fair" rw spinlocks

Andi Kleen
2009-11-28T11:15:04Z

"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:
>
> The usual trick would be to keep per-fair-rwlock state in per-CPU
> variables. If it is forbidden to read-acquire one nestable fair rwlock
> while read-holding another, then this per-CPU state can be a single
> pointer and a nesting count. On the other hand, if it is permitted to
> read-acquire one nestable fair rwlock while holding another, then one
> can use a small per-CPU array of pointer/count pairs.

The problem is that in preemptible kernels kernel threads can switch
CPUs all the time. How would you sync the per CPU state then?

-Andi
--
ak@linux.intel.com -- Speaking for myself only.