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Date: Fri, 14 Aug 2009 21:16:00 +0200
From: Manfred Spraul <manfred@...orfullife.com>
To: npiggin@...e.de
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] [patch 4a/4] ipc: sem optimise simple operations
An alternative patch to Nick's proposal:
http://lkml.org/lkml/2009/8/11/11
The patch is based on Nick's patch.
The patch is ontop of the first three patches from Nick.
Identical with Nick's patch:
- per semaphore list to optimize single sop semop calls:
This avoids that the semaphore operations have to scan through all waiting
tasks, even for the tasks that are waiting on a different semaphore from
the same array.
Differences:
- same code for per-semaphore and global list.
- one list for both wait-for-zero and decrement instead of two lists.
- unlink_queue helper function
Open points:
- further testing
- understand all changes. e.g. why switch from "if (alter)" to
"if (alter & !error)" in update_queue
>From the diffstat, it's simpler: 50 new lines instead of 110 new lines.
Nick: What do you think? Could you try your test app?
Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
---
include/linux/sem.h | 5 ++-
ipc/sem.c | 83 ++++++++++++++++++++++++++++++++++++++++-----------
2 files changed, 69 insertions(+), 19 deletions(-)
diff --git a/include/linux/sem.h b/include/linux/sem.h
index 1b191c1..ea03058 100644
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -86,6 +86,7 @@ struct task_struct;
struct sem {
int semval; /* current value */
int sempid; /* pid of last operation */
+ struct list_head sem_pending; /* pending operations to be processed */
};
/* One sem_array data structure for each set of semaphores in the system. */
@@ -96,11 +97,13 @@ struct sem_array {
struct sem *sem_base; /* ptr to first semaphore in array */
struct list_head sem_pending; /* pending operations to be processed */
struct list_head list_id; /* undo requests on this array */
- unsigned long sem_nsems; /* no. of semaphores in array */
+ int sem_nsems; /* no. of semaphores in array */
+ int complex_count; /* pending complex operations */
};
/* One queue for each sleeping process in the system. */
struct sem_queue {
+ struct list_head simple_list; /* queue of pending operations */
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
diff --git a/ipc/sem.c b/ipc/sem.c
index 3629ef8..495449e 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -240,6 +240,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
key_t key = params->key;
int nsems = params->u.nsems;
int semflg = params->flg;
+ int i;
if (!nsems)
return -EINVAL;
@@ -272,6 +273,14 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
ns->used_sems += nsems;
sma->sem_base = (struct sem *) &sma[1];
+
+ for (i = 0; i < nsems; i++) {
+ struct sem *s = &sma->sem_base[i];
+
+ INIT_LIST_HEAD(&s->sem_pending);
+ }
+
+ sma->complex_count = 0;
INIT_LIST_HEAD(&sma->sem_pending);
INIT_LIST_HEAD(&sma->list_id);
sma->sem_nsems = nsems;
@@ -335,7 +344,7 @@ SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
* all at once. Return 0 if yes, 1 if need to sleep, else return error code.
*/
-static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops,
+static int try_atomic_semop(struct sem_array * sma, struct sembuf * sops,
int nsops, struct sem_undo *un, int pid)
{
int result, sem_op;
@@ -418,15 +427,35 @@ static void wake_up_sem_queue(struct sem_queue *q, int error)
preempt_enable();
}
+static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
+{
+ list_del(&q->list);
+ if (q->nsops == 1) {
+ BUG_ON(list_empty(&q->simple_list));
+ list_del(&q->simple_list);
+ } else {
+ BUG_ON(!list_empty(&q->simple_list));
+ sma->complex_count--;
+ }
+}
+
+
/* Go through the pending queue for the indicated semaphore
* looking for tasks that can be completed.
*/
-static void update_queue (struct sem_array * sma)
+static void update_queue(struct sem_array *sma, int semnum)
{
struct sem_queue *q, *tq;
+ struct list_head *pending_list;
again:
- list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
+ if (semnum == -1 || sma->complex_count) {
+ pending_list = &sma->sem_pending;
+ } else {
+ pending_list = &sma->sem_base[semnum].sem_pending;
+ }
+
+ list_for_each_entry_safe(q, tq, pending_list, list) {
int error;
int alter;
@@ -436,21 +465,21 @@ again:
/* Does q->sleeper still need to sleep? */
if (error > 0)
continue;
+ unlink_queue(sma, q);
- list_del(&q->list);
+ alter = q->alter;
+ wake_up_sem_queue(q, error);
/*
* The next operation that must be checked depends on the type
* of the completed operation:
* - if the operation modified the array, then restart from the
* head of the queue and check for threads that might be
- * waiting for semaphore values to become 0.
+ * waiting for this particular semaphore value.
* - if the operation didn't modify the array, then just
* continue.
*/
- alter = q->alter;
- wake_up_sem_queue(q, error);
- if (alter)
+ if (alter && !error)
goto again;
}
}
@@ -531,8 +560,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
/* Wake up all pending processes and let them fail with EIDRM. */
list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
- list_del(&q->list);
-
+ unlink_queue(sma, q);
wake_up_sem_queue(q, -EIDRM);
}
@@ -754,7 +782,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ update_queue(sma, -1);
err = 0;
goto out_unlock;
}
@@ -796,7 +824,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
curr->sempid = task_tgid_vnr(current);
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ update_queue(sma, semnum);
err = 0;
goto out_unlock;
}
@@ -1169,10 +1197,14 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
if (error)
goto out_unlock_free;
- error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
+ error = try_atomic_semop(sma, sops, nsops, un, task_tgid_vnr(current));
if (error <= 0) {
- if (alter && error == 0)
- update_queue (sma);
+ if (alter && !error) {
+ if (nsops == 1)
+ update_queue(sma, sops->sem_num);
+ else
+ update_queue(sma, -1);
+ }
goto out_unlock_free;
}
@@ -1189,6 +1221,18 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
list_add_tail(&queue.list, &sma->sem_pending);
else
list_add(&queue.list, &sma->sem_pending);
+ if (nsops == 1) {
+ struct sem *curr;
+ curr = &sma->sem_base[sops->sem_num];
+
+ if (alter)
+ list_add_tail(&queue.list, &curr->sem_pending);
+ else
+ list_add(&queue.list, &curr->sem_pending);
+ } else {
+ INIT_LIST_HEAD(&queue.simple_list);
+ sma->complex_count++;
+ }
queue.status = -EINTR;
queue.sleeper = current;
@@ -1231,7 +1275,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
*/
if (timeout && jiffies_left == 0)
error = -EAGAIN;
- list_del(&queue.list);
+ unlink_queue(sma, &queue);
out_unlock_free:
sem_unlock(sma);
@@ -1356,11 +1400,14 @@ void exit_sem(struct task_struct *tsk)
if (semaphore->semval > SEMVMX)
semaphore->semval = SEMVMX;
semaphore->sempid = task_tgid_vnr(current);
+ if (likely(!sma->complex_count))
+ update_queue(sma, i);
}
}
sma->sem_otime = get_seconds();
/* maybe some queued-up processes were waiting for this */
- update_queue(sma);
+ if (unlikely(sma->complex_count))
+ update_queue(sma, -1);
sem_unlock(sma);
call_rcu(&un->rcu, free_un);
@@ -1374,7 +1421,7 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
struct sem_array *sma = it;
return seq_printf(s,
- "%10d %10d %4o %10lu %5u %5u %5u %5u %10lu %10lu\n",
+ "%10d %10d %4o %10u %5u %5u %5u %5u %10lu %10lu\n",
sma->sem_perm.key,
sma->sem_perm.id,
sma->sem_perm.mode,
--
1.6.2.5
--
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