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authorManfred Spraul <manfred@colorfullife.com>2010-05-26 14:43:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-27 09:12:49 -0700
commitc5cf6359ad1d322c16e159011247341849cc0d3a (patch)
treeaefc0ff518c05d5fb386ab2103ec4dc25bffbe4d /mm/highmem.c
parent31a7c4746e9925512afab30557dd445d677cc802 (diff)
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ipc/sem.c: update description of the implementation
ipc/sem.c begins with a 15 year old description about bugs in the initial implementation in Linux-1.0. The patch replaces that with a top level description of the current code. A TODO could be derived from this text: The opengroup man page for semop() does not mandate FIFO. Thus there is no need for a semaphore array list of pending operations. If - this list is removed - the per-semaphore array spinlock is removed (possible if there is no list to protect) - sem_otime is moved into the semaphores and calculated on demand during semctl() then the array would be read-mostly - which would significantly improve scaling for applications that use semaphore arrays with lots of entries. The price would be expensive semctl() calls: for(i=0;i<sma->sem_nsems;i++) spin_lock(sma->sem_lock); <do stuff> for(i=0;i<sma->sem_nsems;i++) spin_unlock(sma->sem_lock); I'm not sure if the complexity is worth the effort, thus here is the documentation of the current behavior first. Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Chris Mason <chris.mason@oracle.com> Cc: Zach Brown <zach.brown@oracle.com> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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