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    SubjectRe: [RFC] time: xtime_lock is held too long
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    Le vendredi 06 mai 2011 à 18:59 +0200, Andi Kleen a écrit :

    > If you have a better way to make it faster please share it.

    Ideally we could use RCU :)

    Have whatever state hold in one structure (possibly big, it doesnt
    matter) and switch pointer in writer once everything is setup in new
    structure.

    struct {
    struct timespec xtime;
    struct timespec wall_to_monotonic;
    ...
    } time_keep_blob;

    struct time_keep_blob __rcu *xtime_cur;

    ktime_t ktime_get(void)
    {
    const struct time_keep_blob *xp;
    s64 secs, nsecs;

    rcu_read_lock();
    xp = rcu_dereference(xtime_cur);
    secs = xp->xtime.tv_sec + xp->wall_to_monotonic.tv_sec;
    nsecs = xp->xtime.tv_nsec + xp->wall_to_monotonic.tv_nsec;
    nsecs += timekeeping_get_ns(xp);
    rcu_read_unlock();

    return ktime_add_ns(ktime_set(secs, 0), nsecs);
    }

    I dont know timekeeping details, maybe its necessary to loop if
    xtime_cur changes :

    ktime_t ktime_get(void)
    {
    const struct time_keep_blob *xp;
    s64 secs, nsecs;

    rcu_read_lock();
    do {
    xp = rcu_dereference(xtime_cur);
    secs = xp->xtime.tv_sec + xp->wall_to_monotonic.tv_sec;
    nsecs = xp->xtime.tv_nsec + xp->wall_to_monotonic.tv_nsec;
    nsecs += timekeeping_get_ns(xp);
    } while (rcu_dereference(xtime_cur) != xp);
    rcu_read_unlock();
    return ktime_add_ns(ktime_set(secs, 0), nsecs);
    }



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