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Subjectipc,sem: sysv semaphore scalability
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Include lkml in the CC: this time... *sigh*
---8<---
This series makes the sysv semaphore code more scalable,
by reducing the time the semaphore lock is held, and making
the locking more scalable for semaphore arrays with multiple
semaphores.

The first four patches were written by Davidlohr Buesso, and
reduce the hold time of the semaphore lock.

The last three patches change the sysv semaphore code locking
to be more fine grained, providing a performance boost when
multiple semaphores in a semaphore array are being manipulated
simultaneously.

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



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