linux-kernel - Re: [RFC] NUMA futex hashing

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Date:	Wed, 09 Aug 2006 11:56:26 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Ulrich Drepper <drepper@...il.com>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] NUMA futex hashing

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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