mappings. Instead, they should be first mapping to an RSS bucket and
then querying the RSS bucket -> CPU ID mapping to figure out the target
CPU.
When (if?) RSS rebalancing is implemented or some other (non round-robin)
distribution of work from buckets to CPU IDs, various bits of code - both
userland and kernel - will need to know how this mapping works.
So, to support this:
* Add a new function rss_m2bucket() - this maps an mbuf to a given bucket.
Anything which is currently doing hash -> CPU work may instead wish to
do hash -> bucket, and then query the bucket->cpuid map for which
CPU it belongs on. Or, map it to a bucket, then re-pin that bucket ->
CPU during a rebalance operation.
* For userland applications which wish to exploit affinity to RSS buckets,
the bucket -> CPU ID mapping is now available via a sysctl.
net.inet.rss.bucket_mapping lists the bucket to CPU ID mapping via
a list of bucket:cpu pairs.
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