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    SubjectRe: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats
    Shailabh Nagar <nagar@watson.ibm.com> wrote:
    >
    > +/*
    > + * Per-task exit data sent from the kernel to user space
    > + * is tagged by an id based on grouping of cpus.
    > + *
    > + * If userspace specifies a non-zero P as the nl_pid field of
    > + * the sockaddr_nl structure while binding to a netlink socket,
    > + * it will receive exit data from threads that exited on cpus in the range
    > + *
    > + * [(P-1)*Y, P*Y-1]
    > + *
    > + * where Y = TASKSTATS_CPUS_PER_SET
    > + * i.e. if TASKSTATS_CPUS_PER_SET is 16,
    > + * to listen to data from cpus 0..15, specify P=1
    > + * for cpus 16..32, specify P=2 etc.
    > + *
    > + * To listen to data from all cpus, userspace should use P=0
    > + */
    > +
    > +#define TASKSTATS_CPUS_PER_SET 16

    The constant is unpleasant.

    If we're going to abuse nl_pid then how about we design things so that
    nl_pid is treated as two 16-bit words - one word is the start CPU and the
    other word is the end cpu?

    Or, if a 65536-CPU limit is too scary, make the bottom 8 bits of nl_pid be
    the number of CPUS (ie: TASKSTATS_CPUS_PER_SET) and the top 24 bits is the
    starting CPU.

    <avoids mentioning nl_pad>

    It'd be better to use a cpumask, of course..
    -
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