• Davidlohr Bueso's avatar
    ipc,shm: introduce lockless functions to obtain the ipc object · 8b8d52ac
    Davidlohr Bueso authored
    This is the third and final patchset that deals with reducing the amount
    of contention we impose on the ipc lock (kern_ipc_perm.lock).  These
    changes mostly deal with shared memory, previous work has already been
    done for semaphores and message queues:
      http://lkml.org/lkml/2013/3/20/546 (sems)
      http://lkml.org/lkml/2013/5/15/584 (mqueues)
    With these patches applied, a custom shm microbenchmark stressing shmctl
    doing IPC_STAT with 4 threads a million times, reduces the execution
    time by 50%.  A similar run, this time with IPC_SET, reduces the
    execution time from 3 mins and 35 secs to 27 seconds.
    Patches 1-8: replaces blindly taking the ipc lock for a smarter
    combination of rcu and ipc_obtain_object, only acquiring the spinlock
    when updating.
    Patch 9: renames the ids rw_mutex to rwsem, which is what it already was.
    Patch 10: is a trivial mqueue leftover cleanup
    Patch 11: adds a brief lock scheme description, requested by Andrew.
    This patch:
    Add shm_obtain_object() and shm_obtain_object_check(), which will allow us
    to get the ipc object without acquiring the lock.  Just as with other
    forms of ipc, these functions are basically wrappers around
    Signed-off-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
    Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Manfred Spraul <manfred@colorfullife.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
shm.c 30.9 KB