Messages in this thread | | | From | Waiman Long <> | Subject | [PATCH v7 0/5] locking/qspinlock: Enhance pvqspinlock performance | Date | Tue, 22 Sep 2015 16:50:39 -0400 |
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v6->v7: - Removed arch/x86/include/asm/qspinlock.h from patch 1. - Removed the unconditional PV kick patch as it has been merged into tip. - Changed the pvstat_inc() API to add a new condition parameter. - Added comments and rearrange code in patch 4 to clarify where lock stealing happened. - In patch 5, removed the check for pv_wait count when deciding when to wait early. - Updated copyrights and email address.
v5->v6: - Added a new patch 1 to relax the cmpxchg and xchg operations in the native code path to reduce performance overhead on non-x86 architectures. - Updated the unconditional PV kick patch as suggested by PeterZ. - Added a new patch to allow one lock stealing attempt at slowpath entry point to reduce performance penalty due to lock waiter preemption. - Removed the pending bit and kick-ahead patches as they didn't show any noticeable performance improvement on top of the lock stealing patch. - Simplified the adaptive spinning patch as the lock stealing patch allows more aggressive pv_wait() without much performance penalty in non-overcommitted VMs.
v4->v5: - Rebased the patch to the latest tip tree. - Corrected the comments and commit log for patch 1. - Removed the v4 patch 5 as PV kick deferment is no longer needed with the new tip tree. - Simplified the adaptive spinning patch (patch 6) & improve its performance a bit further. - Re-ran the benchmark test with the new patch.
v3->v4: - Patch 1: add comment about possible racing condition in PV unlock. - Patch 2: simplified the pv_pending_lock() function as suggested by Davidlohr. - Move PV unlock optimization patch forward to patch 4 & rerun performance test.
v2->v3: - Moved deferred kicking enablement patch forward & move back the kick-ahead patch to make the effect of kick-ahead more visible. - Reworked patch 6 to make it more readable. - Reverted back to use state as a tri-state variable instead of adding an additional bistate variable. - Added performance data for different values of PV_KICK_AHEAD_MAX. - Add a new patch to optimize PV unlock code path performance.
v1->v2: - Take out the queued unfair lock patches - Add a patch to simplify the PV unlock code - Move pending bit and statistics collection patches to the front - Keep vCPU kicking in pv_kick_node(), but defer it to unlock time when appropriate. - Change the wait-early patch to use adaptive spinning to better balance the difference effect on normal and over-committed guests. - Add patch-to-patch performance changes in the patch commit logs.
This patchset tries to improve the performance of both regular and over-commmitted VM guests. The adaptive spinning patch was inspired by the "Do Virtual Machines Really Scale?" blog from Sanidhya Kashyap.
Patch 1 relaxes the memory order restriction of atomic operations by using less restrictive _acquire and _release variants of cmpxchg() and xchg(). This will reduce performance overhead when ported to other non-x86 architectures.
Patch 2 optimizes the PV unlock code path performance for x86-64 architecture.
Patch 3 allows the collection of various count data that are useful to see what is happening in the system. They do add a bit of overhead when enabled slowing performance a tiny bit.
Patch 4 allows one lock stealing attempt at slowpath entry. This causes a pretty big performance improvement for over-committed VM guests.
Patch 5 enables adaptive spinning in the queue nodes. This patch leads to further performance improvement in over-committed guest, though it is not as big as the previous patch.
Waiman Long (5): locking/qspinlock: relaxes cmpxchg & xchg ops in native code locking/pvqspinlock, x86: Optimize PV unlock code path locking/pvqspinlock: Collect slowpath lock statistics locking/pvqspinlock: Allow 1 lock stealing attempt locking/pvqspinlock: Queue node adaptive spinning
arch/x86/Kconfig | 9 + arch/x86/include/asm/qspinlock_paravirt.h | 59 +++++ include/asm-generic/qspinlock.h | 9 +- kernel/locking/qspinlock.c | 48 +++-- kernel/locking/qspinlock_paravirt.h | 376 +++++++++++++++++++++++++---- 5 files changed, 437 insertions(+), 64 deletions(-)
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