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 A were done through:
- 50 us as busy loop timeout
- Netperf 2.6
- Two machines with back to back connected mlx4
- Guest with 8 vcpus and 1 queue
Results:
- TCP_RR was imporved obviously (at most 27%). And cpu utilizaton was
also improved in this case.
- No obvious differences in Guest RX throughput.
- Guest TX throughput was also improved.
TCP_RR:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
1/ 1/ +27%/ 0%/ +27%/ +27%/ +25%
1/ 50/ +2%/ +1%/ +2%/ +2%/ -4%
1/ 100/ +2%/ +1%/ +3%/ +3%/ -14%
1/ 200/ +2%/ +2%/ +5%/ +5%/ -15%
64/ 1/ +20%/ -13%/ +20%/ +20%/ +20%
64/ 50/ +17%/ +14%/ +16%/ +16%/ -11%
64/ 100/ +14%/ +12%/ +14%/ +14%/ -35%
64/ 200/ +16%/ +15%/ +9%/ +9%/ -28%
256/ 1/ +19%/ -6%/ +19%/ +19%/ +18%
256/ 50/ +18%/ +15%/ +16%/ +16%/ +3%
256/ 100/ +11%/ +9%/ +12%/ +12%/ -1%
256/ 200/ +5%/ +8%/ +4%/ +4%/ +64%
512/ 1/ +20%/ 0%/ +20%/ +20%/ -2%
512/ 50/ +12%/ +10%/ +12%/ +12%/ +8%
512/ 100/ +11%/ +7%/ +10%/ +10%/ -5%
512/ 200/ +3%/ +2%/ +3%/ +3%/ -5%
1024/ 1/ +19%/ -2%/ +19%/ +19%/ +18%
1024/ 50/ +13%/ +10%/ +12%/ +12%/ 0%
1024/ 100/ +9%/ +8%/ +8%/ +8%/ -16%
1024/ 200/ +3%/ +4%/ +3%/ +3%/ -14%
Guest RX:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ -12%/ -10%/ +2%/ +1%/ +42%
64/ 4/ -3%/ -5%/ +2%/ -1%/ 0%
64/ 8/ -1%/ -5%/ -1%/ -2%/ 0%
512/ 1/ +5%/ -13%/ +6%/ +9%/ +17%
512/ 4/ -3%/ -9%/ +6%/ +4%/ -14%
512/ 8/ -2%/ -7%/ 0%/ 0%/ -1%
1024/ 1/ +18%/ +31%/ -12%/ -11%/ -31%
1024/ 4/ 0%/ -9%/ -1%/ -6%/ -7%
1024/ 8/ -3%/ -8%/ -2%/ -4%/ 0%
2048/ 1/ 0%/ -1%/ 0%/ -4%/ +5%
2048/ 4/ 0%/ +2%/ 0%/ 0%/ 0%
2048/ 8/ 0%/ -6%/ 0%/ -3%/ -1%
4096/ 1/ -1%/ +2%/ -14%/ -5%/ +8%
4096/ 4/ 0%/ +1%/ 0%/ +1%/ -1%
4096/ 8/ -1%/ -1%/ -2%/ -2%/ -3%
16384/ 1/ 0%/ 0%/ +4%/ +5%/ 0%
16384/ 4/ 0%/ +5%/ +7%/ +9%/ 0%
16384/ 8/ +1%/ +1%/ +3%/ +3%/ +2%
65535/ 1/ 0%/ +12%/ -1%/ +2%/ -2%
65535/ 4/ 0%/ 0%/ -2%/ -2%/ +2%
65535/ 8/ -1%/ -1%/ -4%/ -4%/ 0%
Guest TX:
size/session/+thu%/+normalize%/+tpkts%/+rpkts%/+ioexits%/
64/ 1/ -16%/ -21%/ -2%/ -12%/ +1%
64/ 4/ -6%/ -2%/ -1%/ +6%/ -7%
64/ 8/ +4%/ +4%/ -2%/ +1%/ +30%
512/ 1/ -32%/ -33%/ -11%/ +62%/ +314%
512/ 4/ +30%/ +20%/ -22%/ -17%/ -14%
512/ 8/ +24%/ +12%/ -21%/ -10%/ -6%
1024/ 1/ +1%/ -7%/ +2%/ +51%/ +75%
1024/ 4/ +10%/ +9%/ -11%/ -19%/ -10%
1024/ 8/ +13%/ +7%/ -11%/ -13%/ -12%
2048/ 1/ +17%/ 0%/ +1%/ +35%/ +78%
2048/ 4/ +15%/ +14%/ -17%/ -24%/ -15%
2048/ 8/ +11%/ +9%/ -15%/ -20%/ -12%
4096/ 1/ +3%/ -7%/ 0%/ +21%/ +48%
4096/ 4/ +3%/ +4%/ -9%/ -19%/ +41%
4096/ 8/ +15%/ +13%/ -33%/ -28%/ -15%
16384/ 1/ +5%/ -8%/ -4%/ -10%/ +323%
16384/ 4/ +13%/ +5%/ -15%/ -11%/ +147%
16384/ 8/ +8%/ +6%/ -25%/ -27%/ -31%
65535/ 1/ +8%/ 0%/ +5%/ 0%/ +45%
65535/ 4/ +10%/ +1%/ +7%/ -8%/ +151%
65535/ 8/ +5%/ 0%/ +1%/ -16%/ -29%
Test B were done through:
- 50us as busy loop timeout
- Netperf 2.6
- Two machines with back to back connected ixgbe
- Two guests each wich 1 vcpu and 1 queue
- pin two vhost threads to the same cpu on host to simulate the cpu
contending
Results:
- In this radical case, we can still get at most 14% improvement on
TCP_RR.
- For guest tx stream, minor improvemnt with at most 5% regression in
one byte case. For guest rx stream, at most 5% regression were seen.
Guest TX:
size /-+% /
1 /-5.55%/
64 /+1.11%/
256 /+2.33%/
512 /-0.03%/
1024 /+1.14%/
4096 /+0.00%/
16384/+0.00%/
Guest RX:
size /-+% /
1 /-5.11%/
64 /-0.55%/
256 /-2.35%/
512 /-3.39%/
1024 /+6.8% /
4096 /-0.01%/
16384/+0.00%/
TCP_RR:
size /-+% /
1 /+9.79% /
64 /+4.51% /
256 /+6.47% /
512 /-3.37% /
1024 /+6.15% /
4096 /+14.88%/
16384/-2.23% /
Changes from V2:
- rename vhost_vq_more_avail() to vhost_vq_avail_empty(). And return
false we __get_user() fails.
- do not bother premmptions/timers for good path.
- use vhost_vring_state as ioctl parameter instead of reinveting a new
one.
- add the unit of timeout (us) to the comment of new added ioctls
Changes from V1:
- remove the buggy vq_error() in vhost_vq_more_avail().
- leave vhost_enable_notify() untouched.
Changes from RFC V3:
- small tweak on the code to avoid multiple duplicate conditions in
critical path when busy loop is not enabled.
- add the test result of multiple VMs
Changes from RFC 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 RFC 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_avail_empty()
vhost_net: basic polling support
drivers/vhost/net.c | 79 +++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.c | 35 ++++++++++++++++++++
drivers/vhost/vhost.h | 3 ++
include/uapi/linux/vhost.h | 6 ++++
4 files changed, 118 insertions(+), 5 deletions(-)
--
2.5.0
This path introduces a helper which can give a hint for whether or not
there's a work queued in the work list. This could be used for busy
polling code to exit the busy loop.
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 ad2146a..90ac092 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 d3f7674..43284ad 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);
--
2.5.0
This patch introduces a helper which will return true if we're sure
that the available ring is empty for a specific vq. When we're not
sure, e.g vq access failure, return false instead. This could be used
for busy polling code to exit the busy loop.
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
drivers/vhost/vhost.c | 14 ++++++++++++++
drivers/vhost/vhost.h | 1 +
2 files changed, 15 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 90ac092..c4ff9f2 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1633,6 +1633,20 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
}
EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
+/* return true if we're sure that available ring is empty */
+bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+ __virtio16 avail_idx;
+ int r;
+
+ r = __get_user(avail_idx, &vq->avail->idx);
+ if (r)
+ return false;
+
+ return vhost16_to_cpu(vq, avail_idx) == vq->avail_idx;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
+
/* OK, now we need to know about added descriptors. */
bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 43284ad..a7a43f0 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_avail_empty(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,
--
2.5.0
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 | 79 +++++++++++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.c | 14 ++++++++
drivers/vhost/vhost.h | 1 +
include/uapi/linux/vhost.h | 6 ++++
4 files changed, 95 insertions(+), 5 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9eda69e..c91af93 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -287,6 +287,44 @@ 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);
+ int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+
+ if (r == vq->num && vq->busyloop_timeout) {
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+ while (vhost_can_busy_poll(vq->dev, endtime) &&
+ vhost_vq_avail_empty(vq->dev, vq))
+ cpu_relax();
+ preempt_enable();
+ r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
+ out_num, in_num, NULL, NULL);
+ }
+
+ return r;
+}
+
/* 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 +369,9 @@ 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 +472,38 @@ static int peek_head_len(struct sock *sk)
return len;
}
+static int vhost_net_rx_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);
+ int len = peek_head_len(sk);
+
+ if (!len && vq->busyloop_timeout) {
+ /* Both tx vq and rx socket were polled here */
+ mutex_lock(&vq->mutex);
+ vhost_disable_notify(&net->dev, vq);
+
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+
+ while (vhost_can_busy_poll(&net->dev, endtime) &&
+ skb_queue_empty(&sk->sk_receive_queue) &&
+ vhost_vq_avail_empty(&net->dev, vq))
+ cpu_relax();
+
+ preempt_enable();
+
+ if (vhost_enable_notify(&net->dev, vq))
+ vhost_poll_queue(&vq->poll);
+ mutex_unlock(&vq->mutex);
+
+ len = peek_head_len(sk);
+ }
+
+ return len;
+}
+
/* This is a multi-buffer version of vhost_get_desc, that works if
* vq has read descriptors only.
* @vq - the relevant virtqueue
@@ -553,7 +622,7 @@ 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_rx_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 c4ff9f2..5abfce9 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)
@@ -919,6 +920,19 @@ 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(&s, argp, sizeof(s))) {
+ r = -EFAULT;
+ break;
+ }
+ vq->busyloop_timeout = s.num;
+ break;
+ case VHOST_GET_VRING_BUSYLOOP_TIMEOUT:
+ s.index = idx;
+ s.num = vq->busyloop_timeout;
+ if (copy_to_user(argp, &s, sizeof(s)))
+ r = -EFAULT;
+ break;
default:
r = -ENOIOCTLCMD;
}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a7a43f0..9a02158 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..61a8777 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -126,6 +126,12 @@ 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 (in us) */
+#define VHOST_SET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x23, \
+ struct vhost_vring_state)
+/* Get busy loop timeout (in us) */
+#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \
+ struct vhost_vring_state)
/* VHOST_NET specific defines */
--
2.5.0
David Miller
2016-Feb-26 16:45 UTC
[PATCH V3 0/3] basic busy polling support for vhost_net
From: Jason Wang <jasowang at redhat.com> Date: Fri, 26 Feb 2016 16:42:41 +0800> 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.I'm assuming this will go through Michael's tree.
Michael S. Tsirkin
2016-Feb-28 09:12 UTC
[PATCH V3 0/3] basic busy polling support for vhost_net
On Fri, Feb 26, 2016 at 11:45:02AM -0500, David Miller wrote:> From: Jason Wang <jasowang at redhat.com> > Date: Fri, 26 Feb 2016 16:42:41 +0800 > > > 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. > > I'm assuming this will go through Michael's tree.Definitely.
On Fri, Feb 26, 2016 at 04:42:44PM +0800, Jason Wang wrote:> 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>Looks good overall, but I still see one problem.> --- > drivers/vhost/net.c | 79 +++++++++++++++++++++++++++++++++++++++++++--- > drivers/vhost/vhost.c | 14 ++++++++ > drivers/vhost/vhost.h | 1 + > include/uapi/linux/vhost.h | 6 ++++ > 4 files changed, 95 insertions(+), 5 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 9eda69e..c91af93 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -287,6 +287,44 @@ 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();So I find it quite unfortunate that this still uses single_task_running. This means that for example a SCHED_IDLE task will prevent polling from becoming active, and that seems like a bug, or at least an undocumented feature :). Unfortunately this logic affects the behaviour as observed by userspace, so we can't merge it like this and tune afterwards, since otherwise mangement tools will start depending on this logic.> +} > + > +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); > + int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), > + out_num, in_num, NULL, NULL); > + > + if (r == vq->num && vq->busyloop_timeout) { > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + while (vhost_can_busy_poll(vq->dev, endtime) && > + vhost_vq_avail_empty(vq->dev, vq)) > + cpu_relax(); > + preempt_enable(); > + r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), > + out_num, in_num, NULL, NULL); > + } > + > + return r; > +} > + > /* 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 +369,9 @@ 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 +472,38 @@ static int peek_head_len(struct sock *sk) > return len; > } > > +static int vhost_net_rx_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); > + int len = peek_head_len(sk); > + > + if (!len && vq->busyloop_timeout) { > + /* Both tx vq and rx socket were polled here */ > + mutex_lock(&vq->mutex); > + vhost_disable_notify(&net->dev, vq); > + > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + > + while (vhost_can_busy_poll(&net->dev, endtime) && > + skb_queue_empty(&sk->sk_receive_queue) && > + vhost_vq_avail_empty(&net->dev, vq)) > + cpu_relax(); > + > + preempt_enable(); > + > + if (vhost_enable_notify(&net->dev, vq)) > + vhost_poll_queue(&vq->poll); > + mutex_unlock(&vq->mutex); > + > + len = peek_head_len(sk); > + } > + > + return len; > +} > + > /* This is a multi-buffer version of vhost_get_desc, that works if > * vq has read descriptors only. > * @vq - the relevant virtqueue > @@ -553,7 +622,7 @@ 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_rx_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 c4ff9f2..5abfce9 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) > @@ -919,6 +920,19 @@ 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(&s, argp, sizeof(s))) { > + r = -EFAULT; > + break; > + } > + vq->busyloop_timeout = s.num; > + break; > + case VHOST_GET_VRING_BUSYLOOP_TIMEOUT: > + s.index = idx; > + s.num = vq->busyloop_timeout; > + if (copy_to_user(argp, &s, sizeof(s))) > + r = -EFAULT; > + break; > default: > r = -ENOIOCTLCMD; > } > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index a7a43f0..9a02158 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..61a8777 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -126,6 +126,12 @@ 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 (in us) */ > +#define VHOST_SET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x23, \ > + struct vhost_vring_state) > +/* Get busy loop timeout (in us) */ > +#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \ > + struct vhost_vring_state) > > /* VHOST_NET specific defines */ > > -- > 2.5.0
Christian Borntraeger
2016-Feb-28 21:56 UTC
[PATCH V3 3/3] vhost_net: basic polling support
On 02/26/2016 09:42 AM, Jason Wang wrote:> 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 | 79 +++++++++++++++++++++++++++++++++++++++++++--- > drivers/vhost/vhost.c | 14 ++++++++ > drivers/vhost/vhost.h | 1 + > include/uapi/linux/vhost.h | 6 ++++ > 4 files changed, 95 insertions(+), 5 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 9eda69e..c91af93 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -287,6 +287,44 @@ 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); > + int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), > + out_num, in_num, NULL, NULL); > + > + if (r == vq->num && vq->busyloop_timeout) { > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + while (vhost_can_busy_poll(vq->dev, endtime) && > + vhost_vq_avail_empty(vq->dev, vq)) > + cpu_relax();Can you use cpu_relax_lowlatency (which should be the same as cpu_relax for almost everybody but s390? cpu_relax (without low latency might give up the time slice when running under another hypervisor (like LPAR on s390), which might not be what we want here. [...]> +static int vhost_net_rx_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); > + int len = peek_head_len(sk); > + > + if (!len && vq->busyloop_timeout) { > + /* Both tx vq and rx socket were polled here */ > + mutex_lock(&vq->mutex); > + vhost_disable_notify(&net->dev, vq); > + > + preempt_disable(); > + endtime = busy_clock() + vq->busyloop_timeout; > + > + while (vhost_can_busy_poll(&net->dev, endtime) && > + skb_queue_empty(&sk->sk_receive_queue) && > + vhost_vq_avail_empty(&net->dev, vq)) > + cpu_relax();here as well.
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