Re: [PATCH v12 00/11] qspinlock: a 4-byte queue spinlock with PV support
On 10/24/2014 04:57 AM, Peter Zijlstra wrote: On Thu, Oct 16, 2014 at 02:10:29PM -0400, Waiman Long wrote: v11->v12: - Based on PeterZ's version of the qspinlock patch (https://lkml.org/lkml/2014/6/15/63). - Incorporated many of the review comments from Konrad Wilk and Paolo Bonzini. - The pvqspinlock code is largely from my previous version with PeterZ's way of going from queue tail to head and his idea of using callee saved calls to KVM and XEN codes. Thanks for taking the time to refresh this.. I would prefer you use a little more of the PV techniques I outlined in my latest PV patch to further reduce the overhead of PV enabled kernels on real hardware. This is an important use case, because distro kernels will have to enable PV support while their majority of installations will be on physical hardware. Other than that I see no reason not to move this forward. Thanks for reviewing the patch and agree to move forward. Currently, I am thinking of separating out a PV and non-PV versions of the lock slowpath functions as shown in my previous mail. That should also minimize the performance impact on bare metal even more than what can be done with the PV techniques used in your patch while not penalizing PV performance. As for the unlock function, if the site patching function can handle all the possible call sites of spin_unlock() without disabling function inlining, I will be glad to use your way of handing unlock function. Otherwise, I will prefer my current approach as it is simpler and more easy to understand as well as similar to what has been done in the pv ticket spinlock code. -Longman ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Re: [PATCH v12 00/11] qspinlock: a 4-byte queue spinlock with PV support
On Thu, Oct 16, 2014 at 02:10:29PM -0400, Waiman Long wrote: > v11->v12: > - Based on PeterZ's version of the qspinlock patch >(https://lkml.org/lkml/2014/6/15/63). > - Incorporated many of the review comments from Konrad Wilk and >Paolo Bonzini. > - The pvqspinlock code is largely from my previous version with >PeterZ's way of going from queue tail to head and his idea of >using callee saved calls to KVM and XEN codes. Thanks for taking the time to refresh this.. I would prefer you use a little more of the PV techniques I outlined in my latest PV patch to further reduce the overhead of PV enabled kernels on real hardware. This is an important use case, because distro kernels will have to enable PV support while their majority of installations will be on physical hardware. Other than that I see no reason not to move this forward. ___ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
[PATCH v12 00/11] qspinlock: a 4-byte queue spinlock with PV support
v11->v12: - Based on PeterZ's version of the qspinlock patch (https://lkml.org/lkml/2014/6/15/63). - Incorporated many of the review comments from Konrad Wilk and Paolo Bonzini. - The pvqspinlock code is largely from my previous version with PeterZ's way of going from queue tail to head and his idea of using callee saved calls to KVM and XEN codes. v10->v11: - Use a simple test-and-set unfair lock to simplify the code, but performance may suffer a bit for large guest with many CPUs. - Take out Raghavendra KT's test results as the unfair lock changes may render some of his results invalid. - Add PV support without increasing the size of the core queue node structure. - Other minor changes to address some of the feedback comments. v9->v10: - Make some minor changes to qspinlock.c to accommodate review feedback. - Change author to PeterZ for 2 of the patches. - Include Raghavendra KT's test results in patch 18. v8->v9: - Integrate PeterZ's version of the queue spinlock patch with some modification: http://lkml.kernel.org/r/20140310154236.038181...@infradead.org - Break the more complex patches into smaller ones to ease review effort. - Fix a racing condition in the PV qspinlock code. v7->v8: - Remove one unneeded atomic operation from the slowpath, thus improving performance. - Simplify some of the codes and add more comments. - Test for X86_FEATURE_HYPERVISOR CPU feature bit to enable/disable unfair lock. - Reduce unfair lock slowpath lock stealing frequency depending on its distance from the queue head. - Add performance data for IvyBridge-EX CPU. v6->v7: - Remove an atomic operation from the 2-task contending code - Shorten the names of some macros - Make the queue waiter to attempt to steal lock when unfair lock is enabled. - Remove lock holder kick from the PV code and fix a race condition - Run the unfair lock & PV code on overcommitted KVM guests to collect performance data. v5->v6: - Change the optimized 2-task contending code to make it fairer at the expense of a bit of performance. - Add a patch to support unfair queue spinlock for Xen. - Modify the PV qspinlock code to follow what was done in the PV ticketlock. - Add performance data for the unfair lock as well as the PV support code. v4->v5: - Move the optimized 2-task contending code to the generic file to enable more architectures to use it without code duplication. - Address some of the style-related comments by PeterZ. - Allow the use of unfair queue spinlock in a real para-virtualized execution environment. - Add para-virtualization support to the qspinlock code by ensuring that the lock holder and queue head stay alive as much as possible. v3->v4: - Remove debugging code and fix a configuration error - Simplify the qspinlock structure and streamline the code to make it perform a bit better - Add an x86 version of asm/qspinlock.h for holding x86 specific optimization. - Add an optimized x86 code path for 2 contending tasks to improve low contention performance. v2->v3: - Simplify the code by using numerous mode only without an unfair option. - Use the latest smp_load_acquire()/smp_store_release() barriers. - Move the queue spinlock code to kernel/locking. - Make the use of queue spinlock the default for x86-64 without user configuration. - Additional performance tuning. v1->v2: - Add some more comments to document what the code does. - Add a numerous CPU mode to support >= 16K CPUs - Add a configuration option to allow lock stealing which can further improve performance in many cases. - Enable wakeup of queue head CPU at unlock time for non-numerous CPU mode. This patch set has 3 different sections: 1) Patches 1-6: Introduces a queue-based spinlock implementation that can replace the default ticket spinlock without increasing the size of the spinlock data structure. As a result, critical kernel data structures that embed spinlock won't increase in size and break data alignments. 2) Patch 7: Enables the use of unfair lock in a virtual guest. This can resolve some of the locking related performance issues due to the fact that the next CPU to get the lock may have been scheduled out for a period of time. 3) Patches 8-11: Enable qspinlock para-virtualization support by halting the waiting CPUs after spinning for a certain amount of time. The unlock code will detect the a sleeping waiter and wake it up. This is essentially the same logic as the PV ticketlock code. The queue spinlock has slightly better performance than the ticket spinlock in uncontended case. Its performance can be much better with moderate to heavy contention. This patch has the potential of improving the performance of all the workloads that have moderate to heavy spinlock contention. The queue spinlock is especially suitable for NUMA machines with at least 2 sockets. Thoug
