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authorNick Piggin <npiggin@suse.de>2009-12-15 19:47:28 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-16 10:20:09 -0500
commitbf17bb717759d50a2733a7a8157a7c4a25d93abc (patch)
tree22468665036b37922664529df976c890c5bed2d0 /ipc
parent7d6feeb287c61aafa88f06345387b1188edf4b86 (diff)
ipc/sem.c: sem optimise undo list search
Around a month ago, there was some discussion about an improvement of the sysv sem algorithm: Most (at least: some important) users only use simple semaphore operations, therefore it's worthwile to optimize this use case. This patch: 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> Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Pierre Peiffer <peifferp@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/sem.c26
1 files changed, 20 insertions, 6 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index 2f2a47959576..cb0070ecf5bf 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -962,17 +962,31 @@ static inline int get_undo_list(struct sem_undo_list **undo_listp)
962 return 0; 962 return 0;
963} 963}
964 964
965static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid) 965static struct sem_undo *__lookup_undo(struct sem_undo_list *ulp, int semid)
966{ 966{
967 struct sem_undo *walk; 967 struct sem_undo *un;
968 968
969 list_for_each_entry_rcu(walk, &ulp->list_proc, list_proc) { 969 list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
970 if (walk->semid == semid) 970 if (un->semid == semid)
971 return walk; 971 return un;
972 } 972 }
973 return NULL; 973 return NULL;
974} 974}
975 975
976static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
977{
978 struct sem_undo *un;
979
980 assert_spin_locked(&ulp->lock);
981
982 un = __lookup_undo(ulp, semid);
983 if (un) {
984 list_del_rcu(&un->list_proc);
985 list_add_rcu(&un->list_proc, &ulp->list_proc);
986 }
987 return un;
988}
989
976/** 990/**
977 * find_alloc_undo - Lookup (and if not present create) undo array 991 * find_alloc_undo - Lookup (and if not present create) undo array
978 * @ns: namespace 992 * @ns: namespace
@@ -1308,7 +1322,7 @@ void exit_sem(struct task_struct *tsk)
1308 if (IS_ERR(sma)) 1322 if (IS_ERR(sma))
1309 continue; 1323 continue;
1310 1324
1311 un = lookup_undo(ulp, semid); 1325 un = __lookup_undo(ulp, semid);
1312 if (un == NULL) { 1326 if (un == NULL) {
1313 /* exit_sem raced with IPC_RMID+semget() that created 1327 /* exit_sem raced with IPC_RMID+semget() that created
1314 * exactly the same semid. Nothing to do. 1328 * exactly the same semid. Nothing to do.