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Jason Wang

2015-Nov-12 10:16 UTC

[PATCH net-next RFC V3 0/3] basic busy polling support for vhost_net

Hi all:

This series tries to add basic busy polling for vhost net. The idea is
simple: at the end of tx/rx processing, busy polling for new tx added
descriptor and rx receive socket for a while. The maximum number of
time (in us) could be spent on busy polling was specified ioctl.

Test were done through:

- 50 us as busy loop timeout
- Netperf 2.6
- Two machines with back to back connected ixgbe
- Guest with 1 vcpu and 1 queue

Results:
- For stream workload, ioexits were reduced dramatically in medium
  size (1024-2048) of tx (at most -39%) and almost all rx (at most
  -79%) as a result of polling. This compensate for the possible
  wasted cpu cycles more or less. That porbably why we can still see
  some increasing in the normalized throughput in some cases.
- Throughput of tx were increased (at most 105%) expect for the huge
  write (16384). And we can send more packets in the case (+tpkts were
  increased).
- Very minor rx regression in some cases.
- Improvemnt on TCP_RR (at most 16%).

size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
   64/     1/   +9%/  -17%/   +5%/  +10%/   -2%
   64/     2/   +8%/  -18%/   +6%/  +10%/   -1%
   64/     4/   +4%/  -21%/   +6%/  +10%/   -1%
   64/     8/   +9%/  -17%/   +6%/   +9%/   -2%
  256/     1/  +20%/   -1%/  +15%/  +11%/   -9%
  256/     2/  +15%/   -6%/  +15%/   +8%/   -8%
  256/     4/  +17%/   -4%/  +16%/   +8%/   -8%
  256/     8/  -61%/  -69%/  +16%/  +10%/  -10%
  512/     1/  +15%/   -3%/  +19%/  +18%/  -11%
  512/     2/  +19%/    0%/  +19%/  +13%/  -10%
  512/     4/  +18%/   -2%/  +18%/  +15%/  -10%
  512/     8/  +17%/   -1%/  +18%/  +15%/  -11%
 1024/     1/  +25%/   +4%/  +27%/  +16%/  -21%
 1024/     2/  +28%/   +8%/  +25%/  +15%/  -22%
 1024/     4/  +25%/   +5%/  +25%/  +14%/  -21%
 1024/     8/  +27%/   +7%/  +25%/  +16%/  -21%
 2048/     1/  +32%/  +12%/  +31%/  +22%/  -38%
 2048/     2/  +33%/  +12%/  +30%/  +23%/  -36%
 2048/     4/  +31%/  +10%/  +31%/  +24%/  -37%
 2048/     8/ +105%/  +75%/  +33%/  +23%/  -39%
16384/     1/    0%/  -14%/   +2%/    0%/  +19%
16384/     2/    0%/  -13%/  +19%/  -13%/  +17%
16384/     4/    0%/  -12%/   +3%/    0%/   +2%
16384/     8/    0%/  -11%/   -2%/   +1%/   +1%
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
   64/     1/   -7%/  -23%/   +4%/   +6%/  -74%
   64/     2/   -2%/  -12%/   +2%/   +2%/  -55%
   64/     4/   +2%/   -5%/  +10%/   -2%/  -43%
   64/     8/   -5%/   -5%/  +11%/  -34%/  -59%
  256/     1/   -6%/  -16%/   +9%/  +11%/  -60%
  256/     2/   +3%/   -4%/   +6%/   -3%/  -28%
  256/     4/    0%/   -5%/   -9%/   -9%/  -10%
  256/     8/   -3%/   -6%/  -12%/   -9%/  -40%
  512/     1/   -4%/  -17%/  -10%/  +21%/  -34%
  512/     2/    0%/   -9%/  -14%/   -3%/  -30%
  512/     4/    0%/   -4%/  -18%/  -12%/   -4%
  512/     8/   -1%/   -4%/   -1%/   -5%/   +4%
 1024/     1/    0%/  -16%/  +12%/  +11%/  -10%
 1024/     2/    0%/  -11%/    0%/   +5%/  -31%
 1024/     4/    0%/   -4%/   -7%/   +1%/  -22%
 1024/     8/   -5%/   -6%/  -17%/  -29%/  -79%
 2048/     1/    0%/  -16%/   +1%/   +9%/  -10%
 2048/     2/    0%/  -12%/   +7%/   +9%/  -26%
 2048/     4/    0%/   -7%/   -4%/   +3%/  -64%
 2048/     8/   -1%/   -5%/   -6%/   +4%/  -20%
16384/     1/    0%/  -12%/  +11%/   +7%/  -20%
16384/     2/    0%/   -7%/   +1%/   +5%/  -26%
16384/     4/    0%/   -5%/  +12%/  +22%/  -23%
16384/     8/    0%/   -1%/   -8%/   +5%/   -3%
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
    1/     1/   +9%/  -29%/   +9%/   +9%/   +9%
    1/    25/   +6%/  -18%/   +6%/   +6%/   -1%
    1/    50/   +6%/  -19%/   +5%/   +5%/   -2%
    1/   100/   +5%/  -19%/   +4%/   +4%/   -3%
   64/     1/  +10%/  -28%/  +10%/  +10%/  +10%
   64/    25/   +8%/  -18%/   +7%/   +7%/   -2%
   64/    50/   +8%/  -17%/   +8%/   +8%/   -1%
   64/   100/   +8%/  -17%/   +8%/   +8%/   -1%
  256/     1/  +10%/  -28%/  +10%/  +10%/  +10%
  256/    25/  +15%/  -13%/  +15%/  +15%/    0%
  256/    50/  +16%/  -14%/  +18%/  +18%/   +2%
  256/   100/  +15%/  -13%/  +12%/  +12%/   -2%

Changes from V2:
- poll also at the end of rx handling
- factor out the polling logic and optimize the code a little bit
- add two ioctls to get and set the busy poll timeout
- test on ixgbe (which can give more stable and reproducable numbers)
  instead of mlx4.

Changes from V1:
- Add a comment for vhost_has_work() to explain why it could be
  lockless
- Add param description for busyloop_timeout
- Split out the busy polling logic into a new helper
- Check and exit the loop when there's a pending signal
- Disable preemption during busy looping to make sure lock_clock() was
  correctly used.

Jason Wang (3):
  vhost: introduce vhost_has_work()
  vhost: introduce vhost_vq_more_avail()
  vhost_net: basic polling support

 drivers/vhost/net.c        | 77 +++++++++++++++++++++++++++++++++++++++++++---
 drivers/vhost/vhost.c      | 48 +++++++++++++++++++++++------
 drivers/vhost/vhost.h      |  3 ++
 include/uapi/linux/vhost.h | 11 +++++++
 4 files changed, 125 insertions(+), 14 deletions(-)

-- 
2.1.4

Jason Wang

2015-Nov-12 10:16 UTC

head link

[PATCH net-next RFC V3 1/3] vhost: introduce vhost_has_work()

This path introduces a helper which can give a hint for whether or not
there's a work queued in the work list.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/vhost.c | 7 +++++++
 drivers/vhost/vhost.h | 1 +
 2 files changed, 8 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index eec2f11..163b365 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -245,6 +245,13 @@ void vhost_work_queue(struct vhost_dev *dev, struct
vhost_work *work)
 }
 EXPORT_SYMBOL_GPL(vhost_work_queue);
 
+/* A lockless hint for busy polling code to exit the loop */
+bool vhost_has_work(struct vhost_dev *dev)
+{
+	return !list_empty(&dev->work_list);
+}
+EXPORT_SYMBOL_GPL(vhost_has_work);
+
 void vhost_poll_queue(struct vhost_poll *poll)
 {
 	vhost_work_queue(poll->dev, &poll->work);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 4772862..ea0327d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -37,6 +37,7 @@ struct vhost_poll {
 
 void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);
 void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);
+bool vhost_has_work(struct vhost_dev *dev);
 
 void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
 		     unsigned long mask, struct vhost_dev *dev);
-- 
2.1.4

Jason Wang

2015-Nov-12 10:16 UTC

head link

[PATCH net-next RFC V3 2/3] vhost: introduce vhost_vq_more_avail()

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/vhost.c | 26 +++++++++++++++++---------
 drivers/vhost/vhost.h |  1 +
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 163b365..b86c5aa 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1633,10 +1633,25 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
 }
 EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
 
+bool vhost_vq_more_avail(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+	__virtio16 avail_idx;
+	int r;
+
+	r = __get_user(avail_idx, &vq->avail->idx);
+	if (r) {
+		vq_err(vq, "Failed to check avail idx at %p: %d\n",
+		       &vq->avail->idx, r);
+		return false;
+	}
+
+	return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_more_avail);
+
 /* OK, now we need to know about added descriptors. */
 bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
-	__virtio16 avail_idx;
 	int r;
 
 	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
@@ -1660,14 +1675,7 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct
vhost_virtqueue *vq)
 	/* They could have slipped one in as we were doing that: make
 	 * sure it's written, then check again. */
 	smp_mb();
-	r = __get_user(avail_idx, &vq->avail->idx);
-	if (r) {
-		vq_err(vq, "Failed to check avail idx at %p: %d\n",
-		       &vq->avail->idx, r);
-		return false;
-	}
-
-	return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx;
+	return vhost_vq_more_avail(dev, vq);
 }
 EXPORT_SYMBOL_GPL(vhost_enable_notify);
 
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index ea0327d..5983a13 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -159,6 +159,7 @@ 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_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
+bool vhost_vq_more_avail(struct vhost_dev *, struct vhost_virtqueue *);
 bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
-- 
2.1.4

Jason Wang

2015-Nov-12 10:16 UTC

head link

[PATCH net-next RFC V3 3/3] vhost_net: basic polling support

This patch tries to poll for new added tx buffer or socket receive
queue for a while at the end of tx/rx processing. The maximum time
spent on polling were specified through a new kind of vring ioctl.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/net.c        | 77 +++++++++++++++++++++++++++++++++++++++++++---
 drivers/vhost/vhost.c      | 15 +++++++++
 drivers/vhost/vhost.h      |  1 +
 include/uapi/linux/vhost.h | 11 +++++++
 4 files changed, 99 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9eda69e..a38fa32 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -287,6 +287,45 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf,
bool success)
 	rcu_read_unlock_bh();
 }
 
+static inline unsigned long busy_clock(void)
+{
+	return local_clock() >> 10;
+}
+
+static bool vhost_can_busy_poll(struct vhost_dev *dev,
+				unsigned long endtime)
+{
+	return likely(!need_resched()) &&
+	       likely(!time_after(busy_clock(), endtime)) &&
+	       likely(!signal_pending(current)) &&
+	       !vhost_has_work(dev) &&
+	       single_task_running();
+}
+
+static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
+				    struct vhost_virtqueue *vq,
+				    struct iovec iov[], unsigned int iov_size,
+				    unsigned int *out_num, unsigned int *in_num)
+{
+	unsigned long uninitialized_var(endtime);
+
+	if (vq->busyloop_timeout) {
+		preempt_disable();
+		endtime = busy_clock() + vq->busyloop_timeout;
+	}
+
+	while (vq->busyloop_timeout &&
+	       vhost_can_busy_poll(vq->dev, endtime) &&
+	       !vhost_vq_more_avail(vq->dev, vq))
+		cpu_relax();
+
+	if (vq->busyloop_timeout)
+		preempt_enable();
+
+	return vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+				 out_num, in_num, NULL, NULL);
+}
+
 /* Expects to be always run from workqueue - which acts as
  * read-size critical section for our kind of RCU. */
 static void handle_tx(struct vhost_net *net)
@@ -331,10 +370,9 @@ static void handle_tx(struct vhost_net *net)
 			      % UIO_MAXIOV == nvq->done_idx))
 			break;
 
-		head = vhost_get_vq_desc(vq, vq->iov,
-					 ARRAY_SIZE(vq->iov),
-					 &out, &in,
-					 NULL, NULL);
+		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
+						ARRAY_SIZE(vq->iov),
+						&out, &in);
 		/* On error, stop handling until the next kick. */
 		if (unlikely(head < 0))
 			break;
@@ -435,6 +473,35 @@ static int peek_head_len(struct sock *sk)
 	return len;
 }
 
+static int vhost_net_peek_head_len(struct vhost_net *net, struct sock *sk)
+{
+	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
+	struct vhost_virtqueue *vq = &nvq->vq;
+	unsigned long uninitialized_var(endtime);
+
+	if (vq->busyloop_timeout) {
+		mutex_lock(&vq->mutex);
+		vhost_disable_notify(&net->dev, vq);
+		preempt_disable();
+		endtime = busy_clock() + vq->busyloop_timeout;
+	}
+
+	while (vq->busyloop_timeout &&
+	       vhost_can_busy_poll(&net->dev, endtime) &&
+	       skb_queue_empty(&sk->sk_receive_queue) &&
+	       !vhost_vq_more_avail(&net->dev, vq))
+		cpu_relax();
+
+	if (vq->busyloop_timeout) {
+		preempt_enable();
+		if (vhost_enable_notify(&net->dev, vq))
+			vhost_poll_queue(&vq->poll);
+		mutex_unlock(&vq->mutex);
+	}
+
+	return peek_head_len(sk);
+}
+
 /* This is a multi-buffer version of vhost_get_desc, that works if
  *	vq has read descriptors only.
  * @vq		- the relevant virtqueue
@@ -553,7 +620,7 @@ static void handle_rx(struct vhost_net *net)
 		vq->log : NULL;
 	mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF);
 
-	while ((sock_len = peek_head_len(sock->sk))) {
+	while ((sock_len = vhost_net_peek_head_len(net, sock->sk))) {
 		sock_len += sock_hlen;
 		vhost_len = sock_len + vhost_hlen;
 		headcount = get_rx_bufs(vq, vq->heads, vhost_len,
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b86c5aa..8f9a64c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -285,6 +285,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->memory = NULL;
 	vq->is_le = virtio_legacy_is_little_endian();
 	vhost_vq_reset_user_be(vq);
+	vq->busyloop_timeout = 0;
 }
 
 static int vhost_worker(void *data)
@@ -747,6 +748,7 @@ 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_busyloop_timeout t;
 	u32 idx;
 	long r;
 
@@ -919,6 +921,19 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void
__user *argp)
 	case VHOST_GET_VRING_ENDIAN:
 		r = vhost_get_vring_endian(vq, idx, argp);
 		break;
+	case VHOST_SET_VRING_BUSYLOOP_TIMEOUT:
+		if (copy_from_user(&t, argp, sizeof t)) {
+			r = -EFAULT;
+			break;
+		}
+		vq->busyloop_timeout = t.timeout;
+		break;
+	case VHOST_GET_VRING_BUSYLOOP_TIMEOUT:
+		t.index = idx;
+		t.timeout = vq->busyloop_timeout;
+		if (copy_to_user(argp, &t, sizeof t))
+			r = -EFAULT;
+		break;
 	default:
 		r = -ENOIOCTLCMD;
 	}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 5983a13..90453f0 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -115,6 +115,7 @@ struct vhost_virtqueue {
 	/* Ring endianness requested by userspace for cross-endian support. */
 	bool user_be;
 #endif
+	u32 busyloop_timeout;
 };
 
 struct vhost_dev {
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index ab373191..f013656 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -27,6 +27,11 @@ struct vhost_vring_file {
 
 };
 
+struct vhost_vring_busyloop_timeout {
+	unsigned int index;
+	unsigned int timeout;
+};
+
 struct vhost_vring_addr {
 	unsigned int index;
 	/* Option flags. */
@@ -126,6 +131,12 @@ struct vhost_memory {
 #define VHOST_SET_VRING_CALL _IOW(VHOST_VIRTIO, 0x21, struct vhost_vring_file)
 /* Set eventfd to signal an error */
 #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file)
+/* Set busy loop timeout */
+#define VHOST_SET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x23,	\
+		                     struct vhost_vring_busyloop_timeout)
+/* Get busy loop timeout */
+#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24,	\
+		                     struct vhost_vring_busyloop_timeout)
 
 /* VHOST_NET specific defines */
 
-- 
2.1.4

Jason Wang

2015-Nov-12 10:20 UTC

head link

[PATCH net-next RFC V3 0/3] basic busy polling support for vhost_net

On 11/12/2015 06:16 PM, Jason Wang wrote:> Hi all:
>
> This series tries to add basic busy polling for vhost net. The idea is
> simple: at the end of tx/rx processing, busy polling for new tx added
> descriptor and rx receive socket for a while. The maximum number of
> time (in us) could be spent on busy polling was specified ioctl.
>
> Test were done through:
>
> - 50 us as busy loop timeout
> - Netperf 2.6
> - Two machines with back to back connected ixgbe
> - Guest with 1 vcpu and 1 queue
>
> Results:
> - For stream workload, ioexits were reduced dramatically in medium
>   size (1024-2048) of tx (at most -39%) and almost all rx (at most
>   -79%) as a result of polling. This compensate for the possible
>   wasted cpu cycles more or less. That porbably why we can still see
>   some increasing in the normalized throughput in some cases.
> - Throughput of tx were increased (at most 105%) expect for the huge
>   write (16384). And we can send more packets in the case (+tpkts were
>   increased).
> - Very minor rx regression in some cases.
> - Improvemnt on TCP_RR (at most 16%).
Forget to mention, the following test results by order are:

1) Guest TX
2) Guest RX
3) TCP_RR
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>    64/     1/   +9%/  -17%/   +5%/  +10%/   -2%
>    64/     2/   +8%/  -18%/   +6%/  +10%/   -1%
>    64/     4/   +4%/  -21%/   +6%/  +10%/   -1%
>    64/     8/   +9%/  -17%/   +6%/   +9%/   -2%
>   256/     1/  +20%/   -1%/  +15%/  +11%/   -9%
>   256/     2/  +15%/   -6%/  +15%/   +8%/   -8%
>   256/     4/  +17%/   -4%/  +16%/   +8%/   -8%
>   256/     8/  -61%/  -69%/  +16%/  +10%/  -10%
>   512/     1/  +15%/   -3%/  +19%/  +18%/  -11%
>   512/     2/  +19%/    0%/  +19%/  +13%/  -10%
>   512/     4/  +18%/   -2%/  +18%/  +15%/  -10%
>   512/     8/  +17%/   -1%/  +18%/  +15%/  -11%
>  1024/     1/  +25%/   +4%/  +27%/  +16%/  -21%
>  1024/     2/  +28%/   +8%/  +25%/  +15%/  -22%
>  1024/     4/  +25%/   +5%/  +25%/  +14%/  -21%
>  1024/     8/  +27%/   +7%/  +25%/  +16%/  -21%
>  2048/     1/  +32%/  +12%/  +31%/  +22%/  -38%
>  2048/     2/  +33%/  +12%/  +30%/  +23%/  -36%
>  2048/     4/  +31%/  +10%/  +31%/  +24%/  -37%
>  2048/     8/ +105%/  +75%/  +33%/  +23%/  -39%
> 16384/     1/    0%/  -14%/   +2%/    0%/  +19%
> 16384/     2/    0%/  -13%/  +19%/  -13%/  +17%
> 16384/     4/    0%/  -12%/   +3%/    0%/   +2%
> 16384/     8/    0%/  -11%/   -2%/   +1%/   +1%
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>    64/     1/   -7%/  -23%/   +4%/   +6%/  -74%
>    64/     2/   -2%/  -12%/   +2%/   +2%/  -55%
>    64/     4/   +2%/   -5%/  +10%/   -2%/  -43%
>    64/     8/   -5%/   -5%/  +11%/  -34%/  -59%
>   256/     1/   -6%/  -16%/   +9%/  +11%/  -60%
>   256/     2/   +3%/   -4%/   +6%/   -3%/  -28%
>   256/     4/    0%/   -5%/   -9%/   -9%/  -10%
>   256/     8/   -3%/   -6%/  -12%/   -9%/  -40%
>   512/     1/   -4%/  -17%/  -10%/  +21%/  -34%
>   512/     2/    0%/   -9%/  -14%/   -3%/  -30%
>   512/     4/    0%/   -4%/  -18%/  -12%/   -4%
>   512/     8/   -1%/   -4%/   -1%/   -5%/   +4%
>  1024/     1/    0%/  -16%/  +12%/  +11%/  -10%
>  1024/     2/    0%/  -11%/    0%/   +5%/  -31%
>  1024/     4/    0%/   -4%/   -7%/   +1%/  -22%
>  1024/     8/   -5%/   -6%/  -17%/  -29%/  -79%
>  2048/     1/    0%/  -16%/   +1%/   +9%/  -10%
>  2048/     2/    0%/  -12%/   +7%/   +9%/  -26%
>  2048/     4/    0%/   -7%/   -4%/   +3%/  -64%
>  2048/     8/   -1%/   -5%/   -6%/   +4%/  -20%
> 16384/     1/    0%/  -12%/  +11%/   +7%/  -20%
> 16384/     2/    0%/   -7%/   +1%/   +5%/  -26%
> 16384/     4/    0%/   -5%/  +12%/  +22%/  -23%
> 16384/     8/    0%/   -1%/   -8%/   +5%/   -3%
> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>     1/     1/   +9%/  -29%/   +9%/   +9%/   +9%
>     1/    25/   +6%/  -18%/   +6%/   +6%/   -1%
>     1/    50/   +6%/  -19%/   +5%/   +5%/   -2%
>     1/   100/   +5%/  -19%/   +4%/   +4%/   -3%
>    64/     1/  +10%/  -28%/  +10%/  +10%/  +10%
>    64/    25/   +8%/  -18%/   +7%/   +7%/   -2%
>    64/    50/   +8%/  -17%/   +8%/   +8%/   -1%
>    64/   100/   +8%/  -17%/   +8%/   +8%/   -1%
>   256/     1/  +10%/  -28%/  +10%/  +10%/  +10%
>   256/    25/  +15%/  -13%/  +15%/  +15%/    0%
>   256/    50/  +16%/  -14%/  +18%/  +18%/   +2%
>   256/   100/  +15%/  -13%/  +12%/  +12%/   -2%
>
> Changes from V2:
> - poll also at the end of rx handling
> - factor out the polling logic and optimize the code a little bit
> - add two ioctls to get and set the busy poll timeout
> - test on ixgbe (which can give more stable and reproducable numbers)
>   instead of mlx4.
>
> Changes from V1:
> - Add a comment for vhost_has_work() to explain why it could be
>   lockless
> - Add param description for busyloop_timeout
> - Split out the busy polling logic into a new helper
> - Check and exit the loop when there's a pending signal
> - Disable preemption during busy looping to make sure lock_clock() was
>   correctly used.
>
> Jason Wang (3):
>   vhost: introduce vhost_has_work()
>   vhost: introduce vhost_vq_more_avail()
>   vhost_net: basic polling support
>
>  drivers/vhost/net.c        | 77
+++++++++++++++++++++++++++++++++++++++++++---
>  drivers/vhost/vhost.c      | 48 +++++++++++++++++++++++------
>  drivers/vhost/vhost.h      |  3 ++
>  include/uapi/linux/vhost.h | 11 +++++++
>  4 files changed, 125 insertions(+), 14 deletions(-)
>

Felipe Franciosi

2015-Nov-12 12:02 UTC

head link

[PATCH net-next RFC V3 0/3] basic busy polling support for vhost_net

Hi Jason,

I understand your busy loop timeout is quite conservative at 50us. Did you try
any other values?

Also, did you measure how polling affects many VMs talking to each other (e.g.
20 VMs on each host, perhaps with several vNICs each, transmitting to a
corresponding VM/vNIC pair on another host)?


On a complete separate experiment (busy waiting on storage I/O rings on Xen), I
have observed that bigger timeouts gave bigger benefits. On the other hand, all
cases that contended for CPU were badly hurt with any sort of polling.

The cases that contended for CPU consisted of many VMs generating workload over
very fast I/O devices (in that case, several NVMe devices on a single host). And
the metric that got affected was aggregate throughput from all VMs.

The solution was to determine whether to poll depending on the host's
overall CPU utilisation at that moment. That gave me the best of both worlds as
polling made everything faster without slowing down any other metric.

Thanks,
Felipe



On 12/11/2015 10:20, "kvm-owner at vger.kernel.org on behalf of Jason
Wang" <kvm-owner at vger.kernel.org on behalf of jasowang at
redhat.com> wrote:
>
>
>On 11/12/2015 06:16 PM, Jason Wang wrote:
>> Hi all:
>>
>> This series tries to add basic busy polling for vhost net. The idea is
>> simple: at the end of tx/rx processing, busy polling for new tx added
>> descriptor and rx receive socket for a while. The maximum number of
>> time (in us) could be spent on busy polling was specified ioctl.
>>
>> Test were done through:
>>
>> - 50 us as busy loop timeout
>> - Netperf 2.6
>> - Two machines with back to back connected ixgbe
>> - Guest with 1 vcpu and 1 queue
>>
>> Results:
>> - For stream workload, ioexits were reduced dramatically in medium
>>   size (1024-2048) of tx (at most -39%) and almost all rx (at most
>>   -79%) as a result of polling. This compensate for the possible
>>   wasted cpu cycles more or less. That porbably why we can still see
>>   some increasing in the normalized throughput in some cases.
>> - Throughput of tx were increased (at most 105%) expect for the huge
>>   write (16384). And we can send more packets in the case (+tpkts were
>>   increased).
>> - Very minor rx regression in some cases.
>> - Improvemnt on TCP_RR (at most 16%).
>
>Forget to mention, the following test results by order are:
>
>1) Guest TX
>2) Guest RX
>3) TCP_RR
>
>> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>>    64/     1/   +9%/  -17%/   +5%/  +10%/   -2%
>>    64/     2/   +8%/  -18%/   +6%/  +10%/   -1%
>>    64/     4/   +4%/  -21%/   +6%/  +10%/   -1%
>>    64/     8/   +9%/  -17%/   +6%/   +9%/   -2%
>>   256/     1/  +20%/   -1%/  +15%/  +11%/   -9%
>>   256/     2/  +15%/   -6%/  +15%/   +8%/   -8%
>>   256/     4/  +17%/   -4%/  +16%/   +8%/   -8%
>>   256/     8/  -61%/  -69%/  +16%/  +10%/  -10%
>>   512/     1/  +15%/   -3%/  +19%/  +18%/  -11%
>>   512/     2/  +19%/    0%/  +19%/  +13%/  -10%
>>   512/     4/  +18%/   -2%/  +18%/  +15%/  -10%
>>   512/     8/  +17%/   -1%/  +18%/  +15%/  -11%
>>  1024/     1/  +25%/   +4%/  +27%/  +16%/  -21%
>>  1024/     2/  +28%/   +8%/  +25%/  +15%/  -22%
>>  1024/     4/  +25%/   +5%/  +25%/  +14%/  -21%
>>  1024/     8/  +27%/   +7%/  +25%/  +16%/  -21%
>>  2048/     1/  +32%/  +12%/  +31%/  +22%/  -38%
>>  2048/     2/  +33%/  +12%/  +30%/  +23%/  -36%
>>  2048/     4/  +31%/  +10%/  +31%/  +24%/  -37%
>>  2048/     8/ +105%/  +75%/  +33%/  +23%/  -39%
>> 16384/     1/    0%/  -14%/   +2%/    0%/  +19%
>> 16384/     2/    0%/  -13%/  +19%/  -13%/  +17%
>> 16384/     4/    0%/  -12%/   +3%/    0%/   +2%
>> 16384/     8/    0%/  -11%/   -2%/   +1%/   +1%
>> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>>    64/     1/   -7%/  -23%/   +4%/   +6%/  -74%
>>    64/     2/   -2%/  -12%/   +2%/   +2%/  -55%
>>    64/     4/   +2%/   -5%/  +10%/   -2%/  -43%
>>    64/     8/   -5%/   -5%/  +11%/  -34%/  -59%
>>   256/     1/   -6%/  -16%/   +9%/  +11%/  -60%
>>   256/     2/   +3%/   -4%/   +6%/   -3%/  -28%
>>   256/     4/    0%/   -5%/   -9%/   -9%/  -10%
>>   256/     8/   -3%/   -6%/  -12%/   -9%/  -40%
>>   512/     1/   -4%/  -17%/  -10%/  +21%/  -34%
>>   512/     2/    0%/   -9%/  -14%/   -3%/  -30%
>>   512/     4/    0%/   -4%/  -18%/  -12%/   -4%
>>   512/     8/   -1%/   -4%/   -1%/   -5%/   +4%
>>  1024/     1/    0%/  -16%/  +12%/  +11%/  -10%
>>  1024/     2/    0%/  -11%/    0%/   +5%/  -31%
>>  1024/     4/    0%/   -4%/   -7%/   +1%/  -22%
>>  1024/     8/   -5%/   -6%/  -17%/  -29%/  -79%
>>  2048/     1/    0%/  -16%/   +1%/   +9%/  -10%
>>  2048/     2/    0%/  -12%/   +7%/   +9%/  -26%
>>  2048/     4/    0%/   -7%/   -4%/   +3%/  -64%
>>  2048/     8/   -1%/   -5%/   -6%/   +4%/  -20%
>> 16384/     1/    0%/  -12%/  +11%/   +7%/  -20%
>> 16384/     2/    0%/   -7%/   +1%/   +5%/  -26%
>> 16384/     4/    0%/   -5%/  +12%/  +22%/  -23%
>> 16384/     8/    0%/   -1%/   -8%/   +5%/   -3%
>> size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
>>     1/     1/   +9%/  -29%/   +9%/   +9%/   +9%
>>     1/    25/   +6%/  -18%/   +6%/   +6%/   -1%
>>     1/    50/   +6%/  -19%/   +5%/   +5%/   -2%
>>     1/   100/   +5%/  -19%/   +4%/   +4%/   -3%
>>    64/     1/  +10%/  -28%/  +10%/  +10%/  +10%
>>    64/    25/   +8%/  -18%/   +7%/   +7%/   -2%
>>    64/    50/   +8%/  -17%/   +8%/   +8%/   -1%
>>    64/   100/   +8%/  -17%/   +8%/   +8%/   -1%
>>   256/     1/  +10%/  -28%/  +10%/  +10%/  +10%
>>   256/    25/  +15%/  -13%/  +15%/  +15%/    0%
>>   256/    50/  +16%/  -14%/  +18%/  +18%/   +2%
>>   256/   100/  +15%/  -13%/  +12%/  +12%/   -2%
>>
>> Changes from V2:
>> - poll also at the end of rx handling
>> - factor out the polling logic and optimize the code a little bit
>> - add two ioctls to get and set the busy poll timeout
>> - test on ixgbe (which can give more stable and reproducable numbers)
>>   instead of mlx4.
>>
>> Changes from V1:
>> - Add a comment for vhost_has_work() to explain why it could be
>>   lockless
>> - Add param description for busyloop_timeout
>> - Split out the busy polling logic into a new helper
>> - Check and exit the loop when there's a pending signal
>> - Disable preemption during busy looping to make sure lock_clock() was
>>   correctly used.
>>
>> Jason Wang (3):
>>   vhost: introduce vhost_has_work()
>>   vhost: introduce vhost_vq_more_avail()
>>   vhost_net: basic polling support
>>
>>  drivers/vhost/net.c        | 77
+++++++++++++++++++++++++++++++++++++++++++---
>>  drivers/vhost/vhost.c      | 48 +++++++++++++++++++++++------
>>  drivers/vhost/vhost.h      |  3 ++
>>  include/uapi/linux/vhost.h | 11 +++++++
>>  4 files changed, 125 insertions(+), 14 deletions(-)
>>
>
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