K 10
svn:author
V 7
glebius
K 8
svn:date
V 27
2012-11-23T13:47:41.985848Z
K 7
svn:log
V 975
  Prototype a simple API for per-cpu counters, right now
only 64-bit.

  A counter can be allocated, zeroed, freed, incremented
and decremented.

  The incremention/decremention functions are going to MD.
Right now amd64 implementation is put into MI file, while
the project branch is pre-alpha state.

  A dummy implementation on 64-bit arch would pin to current
CPU, calculate address of counter for this cpu, update it
and unpin. We may provide a racy non-pinning interface, that
can lead the update going to other's CPU counter.

  A smart implementation for amd64 does a one-instruction
update, thus doesn't require any pinning. This is achieved
due to the fact that UMA_ZONE_PCPU zone guarantees us that
per-cpu counters are aligned by the size of struct pcpu
from each other. And we have address of static struct pcpu
in %gs register always. This nice implementation is submitted
by kib@.

  Implementation for 32-bit arches would require critical
section for update.

END