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Subject[RFC PATCH 6/6] cpu-timers: optimize run_posix_cpu_timers()
Date
We can optimize and simplify things taking into account signal->cputimer
is always running when we have configured any process wide cpu timer.

In check_process_timers(), we don't have to check if new updated value
of signal->cputime_expires is smaller, since we maintain new first
expiration time ({prof,virt,sched}_expires) in code flow and all other
writes to expiration cache are protected by sighand->siglock .

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
---
kernel/posix-cpu-timers.c | 81 ++++++++++++++++++---------------------------
1 files changed, 32 insertions(+), 49 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 68d4045..69a9c27 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -995,14 +995,11 @@ static void check_thread_timers(struct task_struct *tsk,
}
}

-static void stop_process_timers(struct task_struct *tsk)
+static void stop_process_timers(struct signal_struct *sig)
{
- struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+ struct thread_group_cputimer *cputimer = &sig->cputimer;
unsigned long flags;

- if (!cputimer->running)
- return;
-
spin_lock_irqsave(&cputimer->lock, flags);
cputimer->running = 0;
spin_unlock_irqrestore(&cputimer->lock, flags);
@@ -1042,6 +1039,23 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
}
}

+/**
+ * task_cputime_zero - Check a task_cputime struct for all zero fields.
+ *
+ * @cputime: The struct to compare.
+ *
+ * Checks @cputime to see if all fields are zero. Returns true if all fields
+ * are zero, false if any field is nonzero.
+ */
+static inline int task_cputime_zero(const struct task_cputime *cputime)
+{
+ if (cputime_eq(cputime->utime, cputime_zero) &&
+ cputime_eq(cputime->stime, cputime_zero) &&
+ cputime->sum_exec_runtime == 0)
+ return 1;
+ return 0;
+}
+
/*
* Check for any per-thread CPU timers that have fired and move them
* off the tsk->*_timers list onto the firing list. Per-thread timers
@@ -1058,19 +1072,6 @@ static void check_process_timers(struct task_struct *tsk,
struct task_cputime cputime;

/*
- * Don't sample the current process CPU clocks if there are no timers.
- */
- if (list_empty(&timers[CPUCLOCK_PROF]) &&
- cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) &&
- sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&
- list_empty(&timers[CPUCLOCK_VIRT]) &&
- cputime_eq(sig->it[CPUCLOCK_VIRT].expires, cputime_zero) &&
- list_empty(&timers[CPUCLOCK_SCHED])) {
- stop_process_timers(tsk);
- return;
- }
-
- /*
* Collect the current process totals.
*/
thread_group_cputimer(tsk, &cputime);
@@ -1157,18 +1158,12 @@ static void check_process_timers(struct task_struct *tsk,
}
}

- if (!cputime_eq(prof_expires, cputime_zero) &&
- (cputime_eq(sig->cputime_expires.prof_exp, cputime_zero) ||
- cputime_gt(sig->cputime_expires.prof_exp, prof_expires)))
- sig->cputime_expires.prof_exp = prof_expires;
- if (!cputime_eq(virt_expires, cputime_zero) &&
- (cputime_eq(sig->cputime_expires.virt_exp, cputime_zero) ||
- cputime_gt(sig->cputime_expires.virt_exp, virt_expires)))
- sig->cputime_expires.virt_exp = virt_expires;
- if (sched_expires != 0 &&
- (sig->cputime_expires.sched_exp == 0 ||
- sig->cputime_expires.sched_exp > sched_expires))
- sig->cputime_expires.sched_exp = sched_expires;
+ sig->cputime_expires.prof_exp = prof_expires;
+ sig->cputime_expires.virt_exp = virt_expires;
+ sig->cputime_expires.sched_exp = sched_expires;
+
+ if (task_cputime_zero(&sig->cputime_expires))
+ stop_process_timers(sig);
}

/*
@@ -1241,23 +1236,6 @@ out:
}

/**
- * task_cputime_zero - Check a task_cputime struct for all zero fields.
- *
- * @cputime: The struct to compare.
- *
- * Checks @cputime to see if all fields are zero. Returns true if all fields
- * are zero, false if any field is nonzero.
- */
-static inline int task_cputime_zero(const struct task_cputime *cputime)
-{
- if (cputime_eq(cputime->utime, cputime_zero) &&
- cputime_eq(cputime->stime, cputime_zero) &&
- cputime->sum_exec_runtime == 0)
- return 1;
- return 0;
-}
-
-/**
* task_cputime_expired - Compare two task_cputime entities.
*
* @sample: The task_cputime structure to be checked for expiration.
@@ -1313,7 +1291,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
}

sig = tsk->signal;
- if (!task_cputime_zero(&sig->cputime_expires)) {
+ if (sig->cputimer.running) {
struct task_cputime group_sample;

thread_group_cputimer(tsk, &group_sample);
@@ -1350,7 +1328,12 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* put them on the firing list.
*/
check_thread_timers(tsk, &firing);
- check_process_timers(tsk, &firing);
+ /*
+ * If there are any active process wide timers (POSIX 1.b, itimers,
+ * RLIMIT_CPU) cputimer must be running.
+ */
+ if (tsk->signal->cputimer.running)
+ check_process_timers(tsk, &firing);

/*
* We must release these locks before taking any timer's lock.
--
1.6.2.5


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