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    Subject[patch 39/44] posix-cpu-timers: Get rid of 64bit divisions
    Instead of dividing A to match the units of B it's more efficient to
    multiply B to match the units of A.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/time/posix-cpu-timers.c | 20 ++++++++++++--------
    1 file changed, 12 insertions(+), 8 deletions(-)

    --- a/kernel/time/posix-cpu-timers.c
    +++ b/kernel/time/posix-cpu-timers.c
    @@ -791,10 +791,11 @@ static void check_thread_timers(struct t
    */
    soft = task_rlimit(tsk, RLIMIT_RTTIME);
    if (soft != RLIM_INFINITY) {
    + /* Task RT timeout is accounted in jiffies. RTTIME is usec */
    + unsigned long rtim = tsk->rt.timeout * (USEC_PER_SEC / HZ);
    unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);

    - if (hard != RLIM_INFINITY &&
    - tsk->rt.timeout > DIV_ROUND_UP(hard, USEC_PER_SEC/HZ)) {
    + if (hard != RLIM_INFINITY && rtim >= hard) {
    /*
    * At the hard limit, we just die.
    * No need to calculate anything else now.
    @@ -806,7 +807,7 @@ static void check_thread_timers(struct t
    __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
    return;
    }
    - if (tsk->rt.timeout > DIV_ROUND_UP(soft, USEC_PER_SEC/HZ)) {
    + if (rtim >= soft) {
    /*
    * At the soft limit, send a SIGXCPU every second.
    */
    @@ -901,11 +902,13 @@ static void check_process_timers(struct

    soft = task_rlimit(tsk, RLIMIT_CPU);
    if (soft != RLIM_INFINITY) {
    + /* RLIMIT_CPU is in seconds. Samples are nanoseconds */
    unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
    - u64 softns, ptime = samples[CPUCLOCK_PROF];
    - unsigned long psecs = div_u64(ptime, NSEC_PER_SEC);
    + u64 ptime = samples[CPUCLOCK_PROF];
    + u64 softns = (u64)soft * NSEC_PER_SEC;
    + u64 hardns = (u64)hard * NSEC_PER_SEC;

    - if (hard != RLIM_INFINITY && psecs >= hard) {
    + if (hard != RLIM_INFINITY && ptime >= hardns) {
    /*
    * At the hard limit, we just die.
    * No need to calculate anything else now.
    @@ -917,7 +920,7 @@ static void check_process_timers(struct
    __group_send_sig_info(SIGKILL, SEND_SIG_PRIV, tsk);
    return;
    }
    - if (psecs >= soft) {
    + if (ptime >= softns) {
    /*
    * At the soft limit, send a SIGXCPU every second.
    */
    @@ -931,7 +934,8 @@ static void check_process_timers(struct
    sig->rlim[RLIMIT_CPU].rlim_cur = soft;
    }
    }
    - softns = soft * NSEC_PER_SEC;
    +
    + /* Update the expiry cache */
    if (softns < exp[CPUCLOCK_PROF])
    exp[CPUCLOCK_PROF] = softns;
    }

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