[patch 39/44] posix-cpu-timers: Get rid of 64bit divisions

[Thomas Gleixner]

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 <t...@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;
        }