v1->v2: - Replace the previous patch that limits the # of times a thread can spin with !lock->owner with a patch that releases the mutex before holding the wait_lock in the __mutex_unlock_common_slowpath() function. - Add a patch which allows a thread to attempt 1 mutex_spin_on_owner() without checking need_resched() if need_resched() triggered while in the MCS queue. - Add a patch which disables preemption between modifying lock->owner and acquiring/releasing the mutex.
This patchset addresses a few scalability issues with mutexes. Patch 1 has the mutex_can_spin_on_owner() funtion check for need_resched() before being added to MCS queue. Patches 2, 3 are to fix issues with threads spinning when there is no lock owner when the mutex is under high contention. Patch 4 and 5 are RFC patches. Patch 4 disables preemption between modifying lock->owner and locking/unlocking the mutex. Patch 5 addresses the situation where spinners can potentially wait a long time in the MCS queue for a chance to spin on mutex owner (not checking for need_resched()), yet ends up not getting to spin. These changes benefit the AIM7 fserver and high_systime workloads (run on disk) on an 8 socket, 80 core box. The table below shows the performance improvements with 3.13 + patches 1, 2, 3 when compared to the 3.13 baseline, and the performance improvements with 3.13 + all 5 patches compared to the 3.13 baseline. Note: I split the % improvement into these 2 categories because patch 3 and patch 5 are the most interesting/important patches in this patchset in terms of performance improvements. --------------------------------------------------------------- high_systime --------------------------------------------------------------- # users | avg % improvement with | avg % improvement with | 3.13 + patch 1, 2, 3 | 3.13 + patch 1, 2, 3, 4, 5 --------------------------------------------------------------- 1000-2000 | +27.05% | +53.35% --------------------------------------------------------------- 100-900 | +36.11% | +52.56% --------------------------------------------------------------- 10-90 | +2.47% | +4.05% --------------------------------------------------------------- --------------------------------------------------------------- fserver --------------------------------------------------------------- # users | avg % improvement with | avg % improvement with | 3.13 + patch 1, 2, 3 | 3.13 + patch 1, 2, 3, 4, 5 --------------------------------------------------------------- 1000-2000 | +18.31% | +37.65% --------------------------------------------------------------- 100-900 | +5.99% | +17.50% --------------------------------------------------------------- 10-90 | +2.47% | +6.10% -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/