[patch 1/4] ipc: sem optimise undo list search

npiggin
2009-08-11T11:56:50Z

[-- Attachment #1: ipc-sem-undo-optimise.patch --]
[-- Type: text/plain, Size: 1766 bytes --]

Move last looked up sem_undo struct to the head of the task's undo list.
Attempt to move common entries to the front of the list so search time is
reduced. This reduces lookup_undo on oprofile of problematic SAP workload
by 30% (see patch 4 for a description of SAP workload).

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
ipc/sem.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)

Index: linux-2.6/ipc/sem.c
===================================================================
--- linux-2.6.orig/ipc/sem.c
+++ linux-2.6/ipc/sem.c
@@ -961,17 +961,31 @@ static inline int get_undo_list(struct s
return 0;
}

-static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
+static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
{
- struct sem_undo *walk;
+ struct sem_undo *un;

- list_for_each_entry_rcu(walk, &ulp->list_proc, list_proc) {
- if (walk->semid == semid)
- return walk;
+ list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
+ if (un->semid == semid)
+ return un;
}
return NULL;
}

+static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
+{
+ struct sem_undo *un;
+
+ assert_spin_locked(&ulp->lock);
+
+ un = __lookup_undo(ulp, semid);
+ if (un) {
+ list_del_rcu(&un->list_proc);
+ list_add_rcu(&un->list_proc, &ulp->list_proc);
+ }
+ return un;
+}
+
/**
* find_alloc_undo - Lookup (and if not present create) undo array
* @ns: namespace
@@ -1307,7 +1321,7 @@ void exit_sem(struct task_struct *tsk)
if (IS_ERR(sma))
continue;

- un = lookup_undo(ulp, semid);
+ un = __lookup_undo(ulp, semid);
if (un == NULL) {
/* exit_sem raced with IPC_RMID+semget() that created
* exactly the same semid. Nothing to do.