KVM: s390: use hrtimer for clock wakeup from idle - v2

This patch reworks the s390 clock comparator wakeup to hrtimer. The clock
comparator is a per-cpu value that is compared against the TOD clock. If
ckc <= TOD an external interrupt 1004 is triggered. Since the clock comparator
and the TOD clock have a much higher resolution than jiffies we should use
hrtimers to trigger the wakeup. This speeds up guest nanosleep for small
values.

Since hrtimers callbacks run in hard-irq context, I added a tasklet to do
the actual work with enabled interrupts.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Christian Ehrhardt <ehrhardt@de.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 23 insertions, 10 deletions

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 4ed4c3a11485..a48830fa9c59 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -12,6 +12,8 @@
 
 #include <asm/lowcore.h>
 #include <asm/uaccess.h>
+#include <linux/hrtimer.h>
+#include <linux/interrupt.h>
 #include <linux/kvm_host.h>
 #include <linux/signal.h>
 #include "kvm-s390.h"
@@ -361,12 +363,10 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
                 return 0;
         }
 
-        sltime = (vcpu->arch.sie_block->ckc - now) / (0xf4240000ul / HZ) + 1;
+        sltime = ((vcpu->arch.sie_block->ckc - now)*125)>>9;
 
-        vcpu->arch.ckc_timer.expires = jiffies + sltime;
-
-        add_timer(&vcpu->arch.ckc_timer);
-        VCPU_EVENT(vcpu, 5, "enabled wait timer:%llx jiffies", sltime);
+        hrtimer_start(&vcpu->arch.ckc_timer, ktime_set (0, sltime) , HRTIMER_MODE_REL);
+        VCPU_EVENT(vcpu, 5, "enabled wait via clock comparator: %llx ns", sltime);
 no_timer:
         spin_lock_bh(&vcpu->arch.local_int.float_int->lock);
         spin_lock_bh(&vcpu->arch.local_int.lock);
@@ -389,21 +389,34 @@ no_timer:
         remove_wait_queue(&vcpu->wq, &wait);
         spin_unlock_bh(&vcpu->arch.local_int.lock);
         spin_unlock_bh(&vcpu->arch.local_int.float_int->lock);
-        del_timer(&vcpu->arch.ckc_timer);
+        hrtimer_try_to_cancel(&vcpu->arch.ckc_timer);
         return 0;
 }
 
-void kvm_s390_idle_wakeup(unsigned long data)
+void kvm_s390_tasklet(unsigned long parm)
 {
-        struct kvm_vcpu *vcpu = (struct kvm_vcpu *)data;
+        struct kvm_vcpu *vcpu = (struct kvm_vcpu *) parm;
 
-        spin_lock_bh(&vcpu->arch.local_int.lock);
+        spin_lock(&vcpu->arch.local_int.lock);
         vcpu->arch.local_int.timer_due = 1;
         if (waitqueue_active(&vcpu->arch.local_int.wq))
                 wake_up_interruptible(&vcpu->arch.local_int.wq);
-        spin_unlock_bh(&vcpu->arch.local_int.lock);
+        spin_unlock(&vcpu->arch.local_int.lock);
 }
 
+/*
+ * low level hrtimer wake routine. Because this runs in hardirq context
+ * we schedule a tasklet to do the real work.
+ */
+enum hrtimer_restart kvm_s390_idle_wakeup(struct hrtimer *timer)
+{
+        struct kvm_vcpu *vcpu;
+
+        vcpu = container_of(timer, struct kvm_vcpu, arch.ckc_timer);
+        tasklet_schedule(&vcpu->arch.tasklet);
+
+        return HRTIMER_NORESTART;
+}
 
 void kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
 {