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    SubjectRe: [PATCH 2/2] hw_breakpoint: Introduce "struct bp_cpuinfo"
    On 06/18, Frederic Weisbecker wrote:
    >
    > On Sun, Jun 02, 2013 at 09:50:57PM +0200, Oleg Nesterov wrote:
    > > This patch simply moves all per-cpu variables into the new single
    > > per-cpu "struct bp_cpuinfo".
    > >
    > > To me this looks more logical and clean, but this can also simplify
    > > the further potential changes. In particular, I do not think this
    > > memory should be per-cpu, it is never used "locally". After this
    > > change it is trivial to turn it into, say, bootmem[nr_cpu_ids].
    > >
    > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    >
    > I'm ok with the patch because it's indeed more logical and clean to pack the info
    > to a single struct.

    Great,

    > But I'm not sure why you think using per-cpu is a problem. It's not only
    > deemed for optimized local uses,

    But it is.

    Simplest example,

    for_each_possible_cpu(cpu)
    total_count = per_cpu(per_cpu_count, cpu);

    Every per_cpu() likely means the cache miss. Not to mention we need the
    additional math to calculate the address of the local counter.

    for_each_possible_cpu(cpu)
    total_count = bootmem_or_kmalloc_array[cpu];

    is much better in this respect.

    And note also that per_cpu_count above can share the cacheline with
    another "hot" per-cpu variable.

    > it's also convenient for allocations and
    > de-allocation, or static definitions.

    Yes, this is advantage. But afaics the only one.

    > I'm not sure why bootmem would make
    > more sense.

    Or kcalloc(nr_cpu_ids), I didn't really mean that alloc_bootmem() is
    necessarily the best option.

    > Other than this in the changelog, the patch is nice, thanks!
    >
    > Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

    Thanks ;)

    Oleg.



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