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

Thomas Gleixner
2019-08-19T15:46:51Z

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;
}