On 8/22/16 12:24 AM, Andres Freund wrote:
Somewhat naïve question from someone with much less clue about low level
cache behaviour trying to follow along: given that we determine such
padding at compile time, how do we ensure that the cacheline size we're
targeting is right at runtime?
There's basically only very few common cacheline sizes. Pretty much only
64 byte and 128 bytes are common these days. By usually padding to the
larger of those two, we waste a bit of memory, but not actually cache
space on platforms with smaller lines, because the padding is never
accessed.
Though, with an N-way associative cache 2x more padding than necessary
cuts the amount you can fit into the cache by half. That could be
meaningful in some cases.
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