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SubjectRe: [patch] Cache align futex hash buckets
Christoph Lameter wrote:
> On Tue, 21 Feb 2006, Nick Piggin wrote:
>
>
>>Ravikiran G Thirumalai wrote:
>>
>>>Following change places each element of the futex_queues hashtable on a
>>>different cacheline. Spinlocks of adjacent hash buckets lie on the same
>>>cacheline otherwise.
>>>
>>
>>It does not make sense to add swaths of unused memory into a hashtable for
>>this purpose, does it?
>
>
> It does if you essentially have a 4k cacheline (because you are doing NUMA
> in software with multiple PCs....) and transferring control of that
> cacheline is comparatively expensive.
>

Instead of 1MB hash with 256 entries in it covering 256 cachelines, you
have a 1MB hash with 65536(ish) entries covering 256 cachelines.

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