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Subject: Ring algorithm with fewer cache misses
Date: Tue, 27 Jun 2023 11:35:43 +0200
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Thread-Topic: Ring algorithm with fewer cache misses
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: <honnappa.nagarahalli@arm.com>, <konstantin.ananyev@huawei.com>,
 <bruce.richardson@intel.com>, "Gavin Hu" <gavin.hu@arm.com>
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Hi Honnappa, Konstantin, Bruce and Gavin,

You might find this ring algorithm optimization article interesting:
https://rigtorp.se/ringbuffer/


It adds the following optimization:

The single-producer put() operation keeps a cache of the consumer's =
index. If the cached consumer index indicates that there was still =
sufficient room in the ring after the previous put() operation, it =
doesn't need to fetch the actual consumer index, and thus avoids a =
potential L1 cache miss (because the actual consumer index is written by =
the consumer threads).

If the cached index doesn't indicate that there is sufficient room in =
the ring, the operation behaves like without the optimization, i.e. it =
proceeds to fetch the actual consumer index (and writes it to its cache) =
and determines if there is sufficient room in the ring.


Similarly, the single-consumer get() operation caches the producer's =
index to determine if there were still sufficient objects present in the =
ring after the previous get() operation.


Med venlig hilsen / Kind regards,
-Morten Br=F8rup