[PATCH 3/6] ipc/sem.c: remove code duplication

Manfred Spraul
2014-05-18T07:58:59Z

count_semzcnt and count_semncnt are more of less identical.
The patch creates a single function that either counts the number of tasks
waiting for zero or waiting due to a decrease operation.

Compared to the initial version, the BUG_ONs were removed.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
ipc/sem.c | 107 ++++++++++++++++++++++++++++++--------------------------------
1 file changed, 51 insertions(+), 56 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index dc648f8..95d5bc5 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -47,8 +47,7 @@
* Thus: Perfect SMP scaling between independent semaphore arrays.
* If multiple semaphores in one array are used, then cache line
* trashing on the semaphore array spinlock will limit the scaling.
- * - semncnt and semzcnt are calculated on demand in count_semncnt() and
- * count_semzcnt()
+ * - semncnt and semzcnt are calculated on demand in count_semcnt()
* - the task that performs a successful semop() scans the list of all
* sleeping tasks and completes any pending operations that can be fulfilled.
* Semaphores are actively given to waiting tasks (necessary for FIFO).
@@ -989,6 +988,31 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
set_semotime(sma, sops);
}

+/*
+ * check_qop: Test how often a queued operation sleeps on the semaphore semnum
+ */
+static int check_qop(struct sem_array *sma, int semnum, struct sem_queue *q,
+ bool count_zero)
+{
+ struct sembuf *sops = q->sops;
+ int nsops = q->nsops;
+ int i, semcnt;
+
+ semcnt = 0;
+
+ for (i = 0; i < nsops; i++) {
+ if (sops[i].sem_num != semnum)
+ continue;
+ if (sops[i].sem_flg & IPC_NOWAIT)
+ continue;
+ if (count_zero && sops[i].sem_op == 0)
+ semcnt++;
+ if (!count_zero && sops[i].sem_op < 0)
+ semcnt++;
+ }
+ return semcnt;
+}
+
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
@@ -998,66 +1022,37 @@ static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsop
* The counts we return here are a rough approximation, but still
* warrant that semncnt+semzcnt>0 if the task is on the pending queue.
*/
-static int count_semncnt(struct sem_array *sma, ushort semnum)
+static int count_semcnt(struct sem_array *sma, ushort semnum,
+ bool count_zero)
{
- int semncnt;
+ struct list_head *l;
struct sem_queue *q;
+ int semcnt;

- semncnt = 0;
- list_for_each_entry(q, &sma->sem_base[semnum].pending_alter, list) {
- struct sembuf *sops = q->sops;
- BUG_ON(sops->sem_num != semnum);
- if ((sops->sem_op < 0) && !(sops->sem_flg & IPC_NOWAIT))
- semncnt++;
- }
-
- list_for_each_entry(q, &sma->pending_alter, list) {
- struct sembuf *sops = q->sops;
- int nsops = q->nsops;
- int i;
- for (i = 0; i < nsops; i++)
- if (sops[i].sem_num == semnum
- && (sops[i].sem_op < 0)
- && !(sops[i].sem_flg & IPC_NOWAIT))
- semncnt++;
- }
- return semncnt;
-}
-
-static int count_semzcnt(struct sem_array *sma, ushort semnum)
-{
- int semzcnt;
- struct sem_queue *q;
+ semcnt = 0;
+ /* First: check the simple operations. They are easy to evaluate */
+ if (count_zero)
+ l = &sma->sem_base[semnum].pending_const;
+ else
+ l = &sma->sem_base[semnum].pending_alter;

- semzcnt = 0;
- list_for_each_entry(q, &sma->sem_base[semnum].pending_const, list) {
- struct sembuf *sops = q->sops;
- BUG_ON(sops->sem_num != semnum);
- if ((sops->sem_op == 0) && !(sops->sem_flg & IPC_NOWAIT))
- semzcnt++;
+ list_for_each_entry(q, l, list) {
+ /* all task on a per-semaphore list sleep on exactly
+ * that semaphore
+ */
+ semcnt++;
}

- list_for_each_entry(q, &sma->pending_const, list) {
- struct sembuf *sops = q->sops;
- int nsops = q->nsops;
- int i;
- for (i = 0; i < nsops; i++)
- if (sops[i].sem_num == semnum
- && (sops[i].sem_op == 0)
- && !(sops[i].sem_flg & IPC_NOWAIT))
- semzcnt++;
- }
+ /* Then: check the complex operations. */
list_for_each_entry(q, &sma->pending_alter, list) {
- struct sembuf *sops = q->sops;
- int nsops = q->nsops;
- int i;
- for (i = 0; i < nsops; i++)
- if (sops[i].sem_num == semnum
- && (sops[i].sem_op == 0)
- && !(sops[i].sem_flg & IPC_NOWAIT))
- semzcnt++;
+ semcnt += check_qop(sma, semnum, q, count_zero);
+ }
+ if (count_zero) {
+ list_for_each_entry(q, &sma->pending_const, list) {
+ semcnt += check_qop(sma, semnum, q, count_zero);
+ }
}
- return semzcnt;
+ return semcnt;
}

/* Free a semaphore set. freeary() is called with sem_ids.rwsem locked
@@ -1459,10 +1454,10 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
err = curr->sempid;
goto out_unlock;
case GETNCNT:
- err = count_semncnt(sma, semnum);
+ err = count_semcnt(sma, semnum, 0);
goto out_unlock;
case GETZCNT:
- err = count_semzcnt(sma, semnum);
+ err = count_semcnt(sma, semnum, 1);
goto out_unlock;
}

--
1.9.0