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    SubjectRe: [thisops uV2 02/10] vmstat: Optimize zone counter modifications through the use of this cpu operations
    On Sat, 27 Nov 2010, Mathieu Desnoyers wrote:

    > * Christoph Lameter ( wrote:
    > > this cpu operations can be used to slightly optimize the function. The
    > > changes will avoid some address calculations and replace them with the
    > > use of the percpu segment register.
    > >
    > > If one would have this_cpu_inc_return and this_cpu_dec_return then it
    > > would be possible to optimize inc_zone_page_state and dec_zone_page_state even
    > > more.
    > Then we might want to directly target the implementation with
    > this_cpu_add_return/this_cpu_sub_return (you implement these in patch 03), which
    > would not need to disable preemption on the fast path. I think we already
    > discussed this in the past. The reason eludes me at the moment, but I remember
    > discussing that changing the increment/decrement delta to the nearest powers of
    > two would let us deal with overflow cleanly. But it's probably too early in the
    > morning for me to wrap my head around the issue at the moment.

    We still would need to disable preemption because multiple this_cpu_ops
    are needed. The only way to avoid preemption would be if the modifications
    to the differential and the adding to the per zone counters would be
    per cpu atomic.

     \ /
      Last update: 2010-11-29 17:19    [W:0.034 / U:117.044 seconds]
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