Re: [RFC] NUMA futex hashing

Nick Piggin
2006-08-09T01:56:32Z

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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