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Wanpeng Li 266e85a5ec KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption Commit `11752adb` (locking/pvqspinlock: Implement hybrid PV queued/unfair locks) introduces hybrid PV queued/unfair locks - queued mode (no starvation) - unfair mode (good performance on not heavily contended lock) The lock waiter goes into the unfair mode especially in VMs with over-commit vCPUs since increaing over-commitment increase the likehood that the queue head vCPU may have been preempted and not actively spinning. However, reschedule queue head vCPU timely to acquire the lock still can get better performance than just depending on lock stealing in over-subscribe scenario. Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM: ebizzy -M vanilla boosting improved 1VM 23520 25040 6% 2VM 8000 13600 70% 3VM 3100 5400 74% The lock holder vCPU yields to the queue head vCPU when unlock, to boost queue head vCPU which is involuntary preemption or the one which is voluntary halt due to fail to acquire the lock after a short spin in the guest. Cc: Waiman Long <longman@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>		2019-07-24 13:56:53 +02:00
Documentation	Documentation: move Documentation/virtual to Documentation/virt	2019-07-24 10:52:11 +02:00
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arch	KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption	2019-07-24 13:56:53 +02:00
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fs	dlm for 5.3	2019-07-12 17:37:53 -07:00
include	Documentation: move Documentation/virtual to Documentation/virt	2019-07-24 10:52:11 +02:00
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kernel	KVM: LAPIC: Inject timer interrupt via posted interrupt	2019-07-20 09:00:40 +02:00
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net	9p pull request for inclusion in 5.13	2019-07-12 17:31:19 -07:00
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tools	Documentation: move Documentation/virtual to Documentation/virt	2019-07-24 10:52:11 +02:00
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virt	Documentation: move Documentation/virtual to Documentation/virt	2019-07-24 10:52:11 +02:00
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MAINTAINERS	Documentation: move Documentation/virtual to Documentation/virt	2019-07-24 10:52:11 +02:00
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README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.