Intel Alder Lake to have CLDEMOTE instruction for faster cache

Posted on Monday, June 08 2020 @ 10:57 CEST by Thomas De Maesschalck
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Word is going around that some of Intel's future architectures, including Alder Lake for the consumer market, Sapphire Rapids for the server market, and Tremont for the low-power market, will receive a new processor instruction called CLDEMOTE. Short for cachine line demote, this feature promises to speed up processor cache performance.
As per definition, “” The CLDEMOTE instruction hints to hardware that the cache line that contains the linear address should be moved(“demoted”) from the cache(s) closest to the processor core to a level more distant from the processor core. This may accelerate subsequent accesses to the line by other cores in the same coherence domain, especially if the line was written by the core that demotes the line.”” The operating system/OS tells the processor core that a specific content of a cache (e.g. cache line) is not required in the lower level cache which is close to this core, and can easily be “demoted” to a higher cache level, but without flushing back to the main system Memory.

“CLDEMOTE” instruction is a “hint” to the hardware that it might help performance to move a cache line from the cache level(s) “closest” to the core to a cache level that is “further” from the core.
DSO Gaming has more details. It's unknown how much performance could be gained with CLDEMOTE.

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