linux/ipc/sem.c, branch v2.6.34

ipc: remove unreachable code in sem.c

2009-12-16T15:20:10Z

This line is unreachable, remove it. [akpm@linux-foundation.org: remove unneeded initialisation of `err'] Signed-off-by: WANG Cong Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: optimize single sops when semval is zero

2009-12-16T15:20:10Z

If multiple simple decrements on the same semaphore are pending, then the current code scans all decrement operations, even if the semaphore value is already 0. The patch optimizes that: if the semaphore value is 0, then there is no need to scan the q->alter entries. Note that this is a common case: It happens if 100 decrements by one are pending and now an increment by one increases the semaphore value from 0 to 1. Without this patch, all 100 entries are scanned. With the patch, only one entry is scanned, then woken up. Then the new rule triggers and the scanning is aborted, without looking at the remaining 99 tasks. With this patch, single sop increment/decrement by 1 are now O(1). (same as with Nick's patch) Signed-off-by: Manfred Spraul Cc: Nick Piggin Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: optimize single semop operations

2009-12-16T15:20:10Z

sysv sem has the concept of semaphore arrays that consist out of multiple semaphores. Atomic operations that affect multiple semaphores are supported. The patch optimizes single semaphore operation calls that affect only one semaphore: It's not necessary to scan all pending operations, it is sufficient to scan the per-semaphore list. The idea is from Nick Piggin version of an ipc sem improvement, the implementation is different: The code tries to keep as much common code as possible. As the result, the patch is simpler, but optimizes fewer cases. Signed-off-by: Manfred Spraul Cc: Nick Piggin Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: add a per-semaphore pending list

2009-12-16T15:20:10Z

Based on Nick's findings: sysv sem has the concept of semaphore arrays that consist out of multiple semaphores. Atomic operations that affect multiple semaphores are supported. The patch is the first step for optimizing simple, single semaphore operations: In addition to the global list of all pending operations, a 2nd, per-semaphore list with the simple operations is added. Note: this patch does not make sense by itself, the new list is used nowhere. Signed-off-by: Manfred Spraul Cc: Nick Piggin Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: optimize if semops fail

2009-12-16T15:20:09Z

Reduce the amount of scanning of the list of pending semaphore operations: If try_atomic_semop failed, then no changes were applied. Thus no need to restart. Additionally, this patch correct an incorrect comment: It's possible to wait for arbitrary semaphore values (do a dec by , wait-for-zero, inc by in one atomic operation) Both changes are from Nick Piggin, the patch is the result of a different split of the individual changes. Signed-off-by: Manfred Spraul Cc: Nick Piggin Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: sem preempt improve

2009-12-16T15:20:09Z

The strange sysv semaphore wakeup scheme has a kind of busy-wait lock involved, which could deadlock if preemption is enabled during the "lock". It is an implementation detail (due to a spinlock being held) that this is actually the case. However if "spinlocks" are made preemptible, or if the sem lock is changed to a sleeping lock for example, then the wakeup would become buggy. So this might be a bugfix for -rt kernels. Imagine waker being preempted by wakee and never clearing IN_WAKEUP -- if wakee has higher RT priority then there is a priority inversion deadlock. Even if there is not a priority inversion to cause a deadlock, then there is still time wasted spinning. Signed-off-by: Nick Piggin Signed-off-by: Manfred Spraul Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: sem use list operations

2009-12-16T15:20:09Z

Replace the handcoded list operations in update_queue() with the standard list_for_each_entry macros. list_for_each_entry_safe() must be used, because list entries can disappear immediately uppon the wakeup event. Signed-off-by: Nick Piggin Signed-off-by: Manfred Spraul Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: sem optimise undo list search

2009-12-16T15:20:09Z

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 Signed-off-by: Manfred Spraul Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc ns: fix memory leak (idr)

2009-12-16T15:20:09Z

We have apparently had a memory leak since 7ca7e564e049d8b350ec9d958ff25eaa24226352 "ipc: store ipcs into IDRs" in 2007. The idr of which 3 exist for each ipc namespace is never freed. This patch simply frees them when the ipcns is freed. I don't believe any idr_remove() are done from rcu (and could therefore be delayed until after this idr_destroy()), so the patch should be safe. Some quick testing showed no harm, and the memory leak fixed. Caught by kmemleak. Signed-off-by: Serge E. Hallyn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

rculist: use list_entry_rcu in places where it's appropriate

2009-04-15T10:05:25Z

Use previously introduced list_entry_rcu instead of an open-coded list_entry + rcu_dereference combination. Signed-off-by: Jiri Pirko Reviewed-by: Paul E. McKenney Cc: dipankar@in.ibm.com LKML-Reference: <20090414181715.GA3634@psychotron.englab.brq.redhat.com> Signed-off-by: Ingo Molnar