[LAD] jackd buffersize

Jussi Laako jussi at sonarnerd.net
Mon May 11 17:49:10 UTC 2009

Jens M Andreasen wrote:
> What is the rationale for jackd requiring buffers to have number of
> frames set to a power of 2? Could this be relaxed to perhaps a multiple
> of 16, 32 or somesuch?

SSE optimizations require, for performance reasons, that buffers are
128-bit aligned. SSE is really slow on non-aligned access and due to
rather small buffers cannot catch up in the performance after getting up
to aligned address. Size itself doesn't have to be anything specific,
but anything which is not multiple of 4 would also cause slow down.
Having some pad bytes (if possible) thus makes it possible to work
around this limitation.

By disabling SIMD optimizations this restriction goes away with some
performance penalty.

	- Jussi

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