Re: [PATCH 7/7] ipc,sem: fine grained locking for semtimedop

[Davidlohr Bueso]

On Wed, 2013-03-20 at 15:55 -0400, Rik van Riel wrote:
> Introduce finer grained locking for semtimedop, to handle the
> common case of a program wanting to manipulate one semaphore
> from an array with multiple semaphores.
> 
> If the call is a semop manipulating just one semaphore in
> an array with multiple semaphores, only take the lock for
> that semaphore itself.
> 
> If the call needs to manipulate multiple semaphores, or
> another caller is in a transaction that manipulates multiple
> semaphores, the sem_array lock is taken, as well as all the
> locks for the individual semaphores.
> 
> On a 24 CPU system, performance numbers with the semop-multi
> test with N threads and N semaphores, look like this:
> 
> 	vanilla		Davidlohr's	Davidlohr's +	Davidlohr's +
> threads			patches		rwlock patches	v3 patches
> 10	610652		726325		1783589		2142206
> 20	341570		365699		1520453		1977878
> 30	288102		307037		1498167		2037995
> 40	290714		305955		1612665		2256484
> 50	288620		312890		1733453		2650292
> 60	289987		306043		1649360		2388008
> 70	291298		306347		1723167		2717486
> 80	290948		305662		1729545		2763582
> 90	290996		306680		1736021		2757524
> 100	292243		306700		1773700		3059159
> 
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

Acked-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx>

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