The patch titled
ipc/sem.c: sem optimise undo list search
has been added to the -mm tree. Its filename is
ipc-semc-sem-optimise-undo-list-search.patch
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Subject: ipc/sem.c: sem optimise undo list search
From: Nick Piggin <npiggin@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Pierre Peiffer <peifferp@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
diff -puN ipc/sem.c~ipc-semc-sem-optimise-undo-list-search ipc/sem.c
--- a/ipc/sem.c~ipc-semc-sem-optimise-undo-list-search
+++ a/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.
_
Patches currently in -mm which might be from npiggin@xxxxxxx are
linux-next.patch
fs-remove-unneeded-dcache_unhashed-tricks.patch
fs-improve-remountro-vs-buffercache-coherency.patch
ipc-semc-sem-optimise-undo-list-search.patch
ipc-semc-sem-use-list-operations.patch
ipc-semc-sem-preempt-improve.patch
ipc-semc-optimize-if-semops-fail.patch
ipc-semc-add-a-per-semaphore-pending-list.patch
ipc-semc-optimize-single-semop-operations.patch
ipc-semc-optimize-single-sops-when-semval-is-zero.patch
reiser4.patch
fs-symlink-write_begin-allocation-context-fix-reiser4-fix.patch
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