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    SubjectRe: [PATCH v2 0/4] implement vcpu preempted check
    On 07/06/2016 02:52 AM, Peter Zijlstra wrote:
    > On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote:
    >> change fomr v1:
    >> a simplier definition of default vcpu_is_preempted
    >> skip mahcine type check on ppc, and add config. remove dedicated macro.
    >> add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner.
    >> add more comments
    >> thanks boqun and Peter's suggestion.
    >>
    >> This patch set aims to fix lock holder preemption issues.
    >>
    >> test-case:
    >> perf record -a perf bench sched messaging -g 400 -p&& perf report
    >>
    >> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock
    >> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner
    >> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock
    >> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task
    >> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq
    >> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is
    >> 2.49% sched-messaging [kernel.vmlinux] [k] system_call
    >>
    >> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin
    >> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner.
    >> These spin_on_onwer variant also cause rcu stall before we apply this patch set
    >>
    > Paolo, could you help out with an (x86) KVM interface for this?
    >
    > Waiman, could you see if you can utilize this to get rid of the
    > SPIN_THRESHOLD in qspinlock_paravirt?

    That API is certainly useful to make the paravirt spinlock perform
    better. However, I am not sure if we can completely get rid of the
    SPIN_THRESHOLD at this point. It is not just the kvm, the xen code need
    to be modified as well.

    Cheers,
    Longman

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