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Commit cc95a07f authored by Eric Dumazet's avatar Eric Dumazet Committed by Peter Zijlstra
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x86/apic: Reduce cache line misses in __x2apic_send_IPI_mask()



Using per-cpu storage for @x86_cpu_to_logical_apicid is not optimal.

Broadcast IPI will need at least one cache line per cpu to access this
field.

__x2apic_send_IPI_mask() is using standard bitmask operators.

By converting x86_cpu_to_logical_apicid to an array, we divide by 16x
number of needed cache lines, because we find 16 values per cache
line. CPU prefetcher can kick nicely.

Also move @cluster_masks to READ_MOSTLY section to avoid false sharing.

Tested on a dual socket host with 256 cpus, cost for a full broadcast
is now 11 usec instead of 33 usec.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211007143556.574911-1-eric.dumazet@gmail.com
parent 3906fe9b
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