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    SubjectRe: [PATCH] use unfair spinlock when running on hypervisor.
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    Le jeudi 03 juin 2010 à 09:50 +0530, Srivatsa Vaddagiri a écrit :
    > On Wed, Jun 02, 2010 at 12:00:27PM +0300, Avi Kivity wrote:
    > >
    > > There are two separate problems: the more general problem is that
    > > the hypervisor can put a vcpu to sleep while holding a lock, causing
    > > other vcpus to spin until the end of their time slice. This can
    > > only be addressed with hypervisor help.
    >
    > Fyi - I have a early patch ready to address this issue. Basically I am using
    > host-kernel memory (mmap'ed into guest as io-memory via ivshmem driver) to hint
    > host whenever guest is in spin-lock'ed section, which is read by host scheduler
    > to defer preemption.
    >
    > Guest side:
    >
    > static inline void spin_lock(spinlock_t *lock)
    > {
    > raw_spin_lock(&lock->rlock);
    > + __get_cpu_var(gh_vcpu_ptr)->defer_preempt++;

    1) __this_cpu_inc() should be faster

    2) Isnt a bit late to do this increment _after_
    raw_spin_lock(&lock->rlock);

    > }
    >
    > static inline void spin_unlock(spinlock_t *lock)
    > {
    > + __get_cpu_var(gh_vcpu_ptr)->defer_preempt--;
    > raw_spin_unlock(&lock->rlock);
    > }



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