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    SubjectRe: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush
    On 01/02/2012 01:59 PM, Gilad Ben-Yossef wrote:
    > On Sun, Jan 1, 2012 at 6:50 PM, Avi Kivity <avi@redhat.com> wrote:
    > > On 01/01/2012 06:12 PM, Gilad Ben-Yossef wrote:
    > >> >
    > >> > Since this seems to be a common pattern, how about:
    > >> >
    > >> > zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC);
    > >> > ...
    > >> > free_cpumask_var(cpus);
    > >> >
    > >> > The long-named function at the top of the block either returns a newly
    > >> > allocated zeroed cpumask, or a static cpumask with all online cpus set.
    > >> > The code in the middle is only allowed to set bits in the cpumask
    > >> > (should be the common usage). free_cpumask_var() needs to check whether
    > >> > the freed object is the static variable.
    > >>
    > >> Thanks for the feedback and advice! I totally agree the repeating
    > >> pattern needs abstracting.
    > >>
    > >> I ended up chosing to try a different abstraction though - basically a wrapper
    > >> on_each_cpu_cond that gets a predicate function to run per CPU to
    > >> build the mask
    > >> to send the IPI to. It seems cleaner to me not having to mess with
    > >> free_cpumask_var
    > >> and it abstracts more of the general pattern.
    > >>
    > >
    > > This converts the algorithm to O(NR_CPUS) from a potentially lower
    > > complexity algorithm. Also, the existing algorithm may not like to be
    > > driven by cpu number. Both are true for kvm.
    > >
    >
    > Right, I was only thinking on my own uses, which are O(NR_CPUS) by nature.
    >
    > I wonder if it would be better to create a safe_cpumask_var type with
    > its own alloc function
    > free and and sset_cpu function but no clear_cpu function so that the
    > compiler will catch
    > cases of trying to clear bits off of such a cpumask?
    >
    > It seems safer and also makes handling the free function easier.
    >
    > Does that makes sense or am I over engineering it? :-)

    It makes sense. Depends on the number of call sites, really. If there
    are several, consolidation helps, also makes it easier to further refactor.

    --
    error compiling committee.c: too many arguments to function



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