This patch implements basic interrupt coalescing support. This is done
by introducing two new per virtqueue parameters:
- max_coalescced_buffers: maximum number of buffers before trying to
issue an interrupt.
- coalesce_usecs: maximum number of microseconds waited if at least
one buffer is pending before trying to issue an interrupt.
A new ioctl was also introduced for userspace to set or get the above
two values.
The number of coalesced buffers were increased in vhost_add_used_n()
and vhost_signal() was modified that it will only try to issue an
interrupt when:
- The number of coalesced buffers exceed or is equal to
max_coalesced_buffes.
- The time since last signal trying exceed or is equal to
coalesce_usecs.
When neither of the above two conditions were met, the interrupt was
delayed and during exit of a round of processing, device specific code
will call vhost_check_coalesce_and_signal() to check the above two
conditions again and schedule a timer for delayed interrupt if the
conditions were still not met.
Signed-off-by: Jason Wang <jasow...@redhat.com>
---
drivers/vhost/vhost.c | 88 ++++++++++++++++++++++++++++++++++++++++++++--
drivers/vhost/vhost.h | 20 +++++++++++
include/uapi/linux/vhost.h | 13 ++++++-
3 files changed, 117 insertions(+), 4 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ee2826..7739112 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -199,6 +199,11 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call = NULL;
vq->log_ctx = NULL;
vq->memory = NULL;
+ vq->coalesce_usecs = ktime_set(0, 0);
+ vq->max_coalesced_buffers = 0;
+ vq->coalesced = 0;
+ vq->last_signal = ktime_get();
+ hrtimer_cancel(&vq->ctimer);
}
static int vhost_worker(void *data)
@@ -291,6 +296,23 @@ static void vhost_dev_free_iovecs(struct vhost_dev *dev)
vhost_vq_free_iovecs(dev->vqs[i]);
}
+void vhost_check_coalesce_and_signal(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq,
+ bool timer);
+static enum hrtimer_restart vhost_ctimer_handler(struct hrtimer *timer)
+{
+ struct vhost_virtqueue *vq =
+ container_of(timer, struct vhost_virtqueue, ctimer);
+
+ if (mutex_trylock(&vq->mutex)) {
+ vhost_check_coalesce_and_signal(vq->dev, vq, false);
+ mutex_unlock(&vq->mutex);
+ } else
+ vhost_poll_queue(&vq->poll);
+
+ return HRTIMER_NORESTART;
+}
+
void vhost_dev_init(struct vhost_dev *dev,
struct vhost_virtqueue **vqs, int nvqs)
{
@@ -315,6 +337,8 @@ void vhost_dev_init(struct vhost_dev *dev,
vq->heads = NULL;
vq->dev = dev;
mutex_init(&vq->mutex);
+ hrtimer_init(&vq->ctimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ vq->ctimer.function = vhost_ctimer_handler;
vhost_vq_reset(dev, vq);
if (vq->handle_kick)
vhost_poll_init(&vq->poll, vq->handle_kick,
@@ -640,6 +664,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void
__user *argp)
struct vhost_vring_state s;
struct vhost_vring_file f;
struct vhost_vring_addr a;
+ struct vhost_vring_coalesce c;
u32 idx;
long r;
@@ -696,6 +721,19 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl,
void __user *argp)
if (copy_to_user(argp, &s, sizeof s))
r = -EFAULT;
break;
+ case VHOST_SET_VRING_COALESCE:
+ if (copy_from_user(&c, argp, sizeof c)) {
+ r = -EFAULT;
+ break;
+ }
+ vq->coalesce_usecs = ns_to_ktime(c.coalesce_usecs *
NSEC_PER_USEC) ;
+ vq->max_coalesced_buffers = c.max_coalesced_buffers;
+ break;
+ case VHOST_GET_VRING_COALESCE:
+ s.index = idx;
+ if (copy_to_user(argp, &c, sizeof c))
+ r = -EFAULT;
+ break;
case VHOST_SET_VRING_ADDR:
if (copy_from_user(&a, argp, sizeof a)) {
r = -EFAULT;
@@ -1415,6 +1453,9 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct
vring_used_elem *heads,
{
int start, n, r;
+ if (vq->max_coalesced_buffers && ktime_to_ns(vq->coalesce_usecs))
+ vq->coalesced += count;
+
start = vq->last_used_idx % vq->num;
n = vq->num - start;
if (n < count) {
@@ -1440,6 +1481,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct
vring_used_elem *heads,
if (vq->log_ctx)
eventfd_signal(vq->log_ctx, 1);
}
+
return r;
}
EXPORT_SYMBOL_GPL(vhost_add_used_n);
@@ -1481,15 +1523,55 @@ static bool vhost_notify(struct vhost_dev *dev, struct
vhost_virtqueue *vq)
return vring_need_event(vhost16_to_cpu(vq, event), new, old);
}
+static void __vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+ if (vq->call_ctx && vhost_notify(dev, vq)) {
+ eventfd_signal(vq->call_ctx, 1);
+ }
+
+ vq->coalesced = 0;
+ vq->last_signal = ktime_get();
+}
+
/* This actually signals the guest, using eventfd. */
void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
- /* Signal the Guest tell them we used something up. */
- if (vq->call_ctx && vhost_notify(dev, vq))
- eventfd_signal(vq->call_ctx, 1);
+ bool can_coalesce = vq->max_coalesced_buffers &&
+ ktime_to_ns(vq->coalesce_usecs);
+
+ if (can_coalesce) {
+ ktime_t passed = ktime_sub(ktime_get(), vq->last_signal);
+
+ if ((vq->coalesced >= vq->max_coalesced_buffers) ||
+ !ktime_before(passed, vq->coalesce_usecs))
+ __vhost_signal(dev, vq);
+ } else {
+ __vhost_signal(dev, vq);
+ }
}
EXPORT_SYMBOL_GPL(vhost_signal);
+void vhost_check_coalesce_and_signal(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq,
+ bool timer)
+{
+ bool can_coalesce = vq->max_coalesced_buffers &&
+ ktime_to_ns(vq->coalesce_usecs);
+
+ hrtimer_try_to_cancel(&vq->ctimer);
+ if (can_coalesce && vq->coalesced) {
+ ktime_t passed = ktime_sub(ktime_get(), vq->last_signal);
+ ktime_t left = ktime_sub(vq->coalesce_usecs, passed);
+
+ if (ktime_to_ns(left) <= 0) {
+ __vhost_signal(dev, vq);
+ } else if (timer) {
+ hrtimer_start(&vq->ctimer, left, HRTIMER_MODE_REL);
+ }
+ }
+}
+EXPORT_SYMBOL_GPL(vhost_check_coalesce_and_signal);
+
/* And here's the combo meal deal. Supersize me! */
void vhost_add_used_and_signal(struct vhost_dev *dev,
struct vhost_virtqueue *vq,
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 8c1c792..2e6754d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -92,6 +92,23 @@ struct vhost_virtqueue {
/* Last used index value we have signalled on */
bool signalled_used_valid;
+ /* Maxinum microseconds waited after at least one buffer is
+ * processed before generating an interrupt.
+ */
+ ktime_t coalesce_usecs;
+
+ /* Maxinum number of pending buffers before genearting an interrupt. */
+ __u32 max_coalesced_buffers;
+
+ /* The number of buffers whose interrupt are coalesced */
+ __u32 coalesced;
+
+ /* Last time we singalled guest. */
+ ktime_t last_signal;
+
+ /* Timer used to trigger an coalesced interrupt. */
+ struct hrtimer ctimer;
+
/* Log writes to used structure. */
bool log_used;
u64 log_addr;
@@ -149,6 +166,9 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct
vhost_virtqueue *,
void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
struct vring_used_elem *heads, unsigned count);
void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
+void vhost_check_coalesce_and_signal(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq,
+ bool timer);
void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index bb6a5b4..6362e6e 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -27,6 +27,12 @@ struct vhost_vring_file {
};
+struct vhost_vring_coalesce {
+ unsigned int index;
+ __u32 coalesce_usecs;
+ __u32 max_coalesced_buffers;
+};
+
struct vhost_vring_addr {
unsigned int index;
/* Option flags. */
@@ -102,7 +108,12 @@ struct vhost_memory {
#define VHOST_SET_VRING_BASE _IOW(VHOST_VIRTIO, 0x12, struct vhost_vring_state)
/* Get accessor: reads index, writes value in num */
#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct
vhost_vring_state)
-
+/* Set coalescing parameters for the ring. */
+#define VHOST_SET_VRING_COALESCE _IOW(VHOST_VIRTIO, 0x13, \
+ struct vhost_vring_coalesce)
+/* Get coalescing parameters for the ring. */
+#define VHOST_GET_VRING_COALESCE _IOW(VHOST_VIRTIO, 0x14, \
+ struct vhost_vring_coalesce)
/* The following ioctls use eventfd file descriptors to signal and poll
* for events. */
--
1.8.3.1
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