Re: [RFC] NUMA futex hashing

From: Nick Piggin
Date: Tue Aug 08 2006 - 21:54:18 EST

Eric Dumazet wrote:

On Tuesday 08 August 2006 18:34, Nick Piggin wrote:

Eric Dumazet wrote:

We certainly can. But if you insist of using mmap sem at all, then we
have a problem.

rbtree would not reduce cacheline bouncing, so :

We could use a hashtable (allocated on demand) of size N, N depending on
NR_CPUS for example. each chain protected by a private spinlock. If N is
well chosen, we might reduce lock cacheline bouncing. (different threads
fighting on different private futexes would have a good chance to get
different cachelines in this hashtable)

See other mail. We already have a hash table ;)

Yes but still you want at FUTEX_WAIT time to tell the kernel the futex is private to this process.

Yes, but I'm saying we already have a hash table. The hash table.

I'm *not* saying you *don't* also want a private directive from userspace.

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