On 04/24/2012 03:55 PM, Christian Borntraeger wrote:
> From: Konstantin Weitz <WEITZKON@xxxxxxxxxx>
>
> This patch implements the directed yield hypercall found on other
> System z hypervisors. It delegates execution time to the virtual cpu
> specified in the instruction's parameter.
>
> Useful to avoid long spinlock waits in the guest.
>
>
> struct kvm_s390_io_info {
> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
> index a353f0e..022962b 100644
> --- a/arch/s390/kvm/diag.c
> +++ b/arch/s390/kvm/diag.c
> @@ -53,6 +53,45 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
> +{
> + struct kvm *kvm = vcpu->kvm;
> + struct kvm_vcpu *tcpu;
> + int tid;
> + int i;
> +
> + tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
> + vcpu->stat.diagnose_9c++;
> + VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d", tid);
> +
> + if (tid == vcpu->vcpu_id)
> + return 0;
> +
> + kvm_for_each_vcpu(i, tcpu, kvm) {
> + if (tcpu->vcpu_id == tid) {
> + struct task_struct *task = NULL;
> + struct pid *pid;
> + rcu_read_lock();
> + pid = rcu_dereference(tcpu->pid);
> + if (pid)
> + task = get_pid_task(tcpu->pid, PIDTYPE_PID);
> + rcu_read_unlock();
> + if (!task)
> + break;
> + if (task->flags & PF_VCPU) {
> + put_task_struct(task);
> + break;
> + }
> + if (yield_to(task, 1)) {
> + put_task_struct(task);
> + return 0;
> + }
> + put_task_struct(task);
> + }
> + }
> + return 0;
> +}
> +
>
I think the code will me more readable, and less obvious that is was
copied from kvm_vcpu_on_spin(), if you put all the processing outside
the loop, except for matching the vpu itself.
So the code reads
find a vcpu
obtain the task
do the yield
instead of looking like you're doing the processing for every vcpu. The
loop is just a slow lookup which might some day be replaced by a table
lookup.
--
error compiling committee.c: too many arguments to function
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