From: Rik van Riel <[email protected]> When running a microbenchmark calling an invalid syscall number in a loop, on a nohz_full CPU, we spend a full 9% of our CPU time in __acct_update_integrals.
This function converts cputime_t to jiffies, to a timeval, only to convert the timeval back to microseconds before discarding it. This patch leaves __acct_update_integrals functionally equivalent, but speeds things up by about 11%, with 10 million calls to an invalid syscall number dropping from 3.7 to 3.3 seconds. Signed-off-by: Rik van Riel <[email protected]> --- kernel/tsacct.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/tsacct.c b/kernel/tsacct.c index 975cb49e32bf..afb5cf8ecc5f 100644 --- a/kernel/tsacct.c +++ b/kernel/tsacct.c @@ -125,22 +125,22 @@ static void __acct_update_integrals(struct task_struct *tsk, { if (likely(tsk->mm)) { cputime_t time, dtime; - struct timeval value; unsigned long flags; - u64 delta; + u64 delta, usecs; local_irq_save(flags); time = stime + utime; dtime = time - tsk->acct_timexpd; - jiffies_to_timeval(cputime_to_jiffies(dtime), &value); - delta = value.tv_sec; - delta = delta * USEC_PER_SEC + value.tv_usec; + delta = cputime_to_jiffies(dtime); if (delta == 0) goto out; + + usecs = jiffies_to_usecs(delta); + tsk->acct_timexpd = time; - tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm); - tsk->acct_vm_mem1 += delta * tsk->mm->total_vm; + tsk->acct_rss_mem1 += usecs * get_mm_rss(tsk->mm); + tsk->acct_vm_mem1 += usecs * tsk->mm->total_vm; out: local_irq_restore(flags); } -- 2.5.0
