On Sat, 2 Apr 2016, Peter Zijlstra wrote:
> On Sat, Apr 02, 2016 at 11:09:18AM -0000, Thomas Gleixner wrote:
> > +/**
> > + * hash_local_futex - Return the hash bucket in the task local cache
> > + * @uaddr: The user space address of the futex
> > + * @prime: The prime number for the modulo operation
> > + *
> > + * That's a primitive hash function, but it turned out to be the most
> > + * efficient one for the task local cache as we don't have anything to
> > + * mix in like we have for the global hash.
> > + */
> > +static inline unsigned int
> > +hash_local_futex(void __user *uaddr, unsigned int prime)
> > +{
> > + return ((unsigned long) uaddr) % prime;
> > +}
>
> > +static unsigned int hash_prime(unsigned int size)
> > +{
> > + switch(size) {
> > + case 16:
> > + default: return 13;
> > + case 32: return 31;
> > + case 64: return 61;
> > + case 128: return 127;
> > + case 256: return 251;
> > + case 512: return 509;
> > + case 1024: return 1021;
> > + case 2048: return 2039;
> > + case 4096: return 4093;
> > + }
> > +}
>
> One wonders what's wrong with include/linux/hash.h ? It appears to me
> hash_ptr() is pretty much what you want, no?
Nothing is wrong with that. Just my futex fried brain not being able to see
the obvious:)
Thanks,
tglx
