* [PATCH v2] vhost: Add polling mode
[not found] <1406807370-razya@il.ibm.com>
@ 2014-07-31 11:50 ` Razya Ladelsky
2014-08-04 14:24 ` Michael S. Tsirkin
0 siblings, 1 reply; 2+ messages in thread
From: Razya Ladelsky @ 2014-07-31 11:50 UTC (permalink / raw)
To: mst, kvm; +Cc: GLIKSON, ERANRA, YOSSIKU, JOELN, abel.gordon
Resubmitting the patch in: http://marc.info/?l=kvm&m=140594903520308&w=2
after fixing the whitespaces issues.
Thank you,
Razya
>From f293e470b36ff9eb4910540c620315c418e4a8fc Mon Sep 17 00:00:00 2001
From: Razya Ladelsky <razya@il.ibm.com>
Date: Thu, 31 Jul 2014 09:47:20 +0300
Subject: [PATCH] vhost: Add polling mode
Add an optional polling mode to continuously poll the virtqueues
for new buffers, and avoid asking the guest to kick us.
Signed-off-by: Razya Ladelsky <razya@il.ibm.com>
---
drivers/vhost/net.c | 6 +-
drivers/vhost/scsi.c | 6 +-
drivers/vhost/vhost.c | 245 +++++++++++++++++++++++++++++++++++++++++++++++--
drivers/vhost/vhost.h | 38 +++++++-
4 files changed, 277 insertions(+), 18 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 971a760..558aecb 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct file *f)
}
vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
- vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
- vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
+ vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT,
+ vqs[VHOST_NET_VQ_TX]);
+ vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN,
+ vqs[VHOST_NET_VQ_RX]);
f->private_data = n;
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 4f4ffa4..665eeeb 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1528,9 +1528,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
if (!vqs)
goto err_vqs;
- vhost_work_init(&vs->vs_completion_work, vhost_scsi_complete_cmd_work);
- vhost_work_init(&vs->vs_event_work, tcm_vhost_evt_work);
-
+ vhost_work_init(&vs->vs_completion_work, NULL,
+ vhost_scsi_complete_cmd_work);
+ vhost_work_init(&vs->vs_event_work, NULL, tcm_vhost_evt_work);
vs->vs_events_nr = 0;
vs->vs_events_missed = false;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c90f437..fbe8174 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -24,9 +24,17 @@
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/cgroup.h>
+#include <linux/jiffies.h>
#include <linux/module.h>
#include "vhost.h"
+static int poll_start_rate = 0;
+module_param(poll_start_rate, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of virtqueue when rate of events is at least this number per jiffy. If 0, never start polling.");
+
+static int poll_stop_idle = 3*HZ; /* 3 seconds */
+module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling of virtqueue after this many jiffies of no work.");
enum {
VHOST_MEMORY_MAX_NREGIONS = 64,
@@ -58,27 +66,28 @@ static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
return 0;
}
-void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
+void vhost_work_init(struct vhost_work *work, struct vhost_virtqueue *vq,
+ vhost_work_fn_t fn)
{
INIT_LIST_HEAD(&work->node);
work->fn = fn;
init_waitqueue_head(&work->done);
work->flushing = 0;
work->queue_seq = work->done_seq = 0;
+ work->vq = vq;
}
EXPORT_SYMBOL_GPL(vhost_work_init);
/* Init poll structure */
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
- unsigned long mask, struct vhost_dev *dev)
+ unsigned long mask, struct vhost_virtqueue *vq)
{
init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
init_poll_funcptr(&poll->table, vhost_poll_func);
poll->mask = mask;
- poll->dev = dev;
+ poll->dev = vq->dev;
poll->wqh = NULL;
-
- vhost_work_init(&poll->work, fn);
+ vhost_work_init(&poll->work, vq, fn);
}
EXPORT_SYMBOL_GPL(vhost_poll_init);
@@ -174,6 +183,86 @@ void vhost_poll_queue(struct vhost_poll *poll)
}
EXPORT_SYMBOL_GPL(vhost_poll_queue);
+/* Enable or disable virtqueue polling (vqpoll.enabled) for a virtqueue.
+ *
+ * Enabling this mode it tells the guest not to notify ("kick") us when its
+ * has made more work available on this virtqueue; Rather, we will continuously
+ * poll this virtqueue in the worker thread. If multiple virtqueues are polled,
+ * the worker thread polls them all, e.g., in a round-robin fashion.
+ * Note that vqpoll.enabled doesn't always mean that this virtqueue is
+ * actually being polled: The backend (e.g., net.c) may temporarily disable it
+ * using vhost_disable/enable_notify(), while vqpoll.enabled is unchanged.
+ *
+ * It is assumed that these functions are called relatively rarely, when vhost
+ * notices that this virtqueue's usage pattern significantly changed in a way
+ * that makes polling more efficient than notification, or vice versa.
+ * Also, we assume that vhost_vq_disable_vqpoll() is always called on vq
+ * cleanup, so any allocations done by vhost_vq_enable_vqpoll() can be
+ * reclaimed.
+ */
+static void vhost_vq_enable_vqpoll(struct vhost_virtqueue *vq)
+{
+ if (vq->vqpoll.enabled)
+ return; /* already enabled, nothing to do */
+ if (!vq->handle_kick)
+ return; /* polling will be a waste of time if no callback! */
+ if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) {
+ /* vq has guest notifications enabled. Disable them,
+ and instead add vq to the polling list */
+ vhost_disable_notify(vq->dev, vq);
+ list_add_tail(&vq->vqpoll.link, &vq->dev->vqpoll_list);
+ }
+ vq->vqpoll.jiffies_last_kick = jiffies;
+ __get_user(vq->avail_idx, &vq->avail->idx);
+ vq->vqpoll.enabled = true;
+
+ /* Map userspace's vq->avail to the kernel's memory space. */
+ if (get_user_pages_fast((unsigned long)vq->avail, 1, 0,
+ &vq->vqpoll.avail_page) != 1) {
+ /* TODO: can this happen, as we check access
+ to vq->avail in advance? */
+ BUG();
+ }
+ vq->vqpoll.avail_mapped = (struct vring_avail *) (
+ (unsigned long)kmap(vq->vqpoll.avail_page) |
+ ((unsigned long)vq->avail & ~PAGE_MASK));
+}
+
+/*
+ * This function doesn't always succeed in changing the mode. Sometimes
+ * a temporary race condition prevents turning on guest notifications, so
+ * vq should be polled next time again.
+ */
+static void vhost_vq_disable_vqpoll(struct vhost_virtqueue *vq)
+{
+ if (!vq->vqpoll.enabled)
+ return; /* already disabled, nothing to do */
+
+ vq->vqpoll.enabled = false;
+
+ if (!list_empty(&vq->vqpoll.link)) {
+ /* vq is on the polling list, remove it from this list and
+ * instead enable guest notifications. */
+ list_del_init(&vq->vqpoll.link);
+ if (unlikely(vhost_enable_notify(vq->dev, vq))
+ && !vq->vqpoll.shutdown) {
+ /* Race condition: guest wrote before we enabled
+ * notification, so we'll never get a notification for
+ * this work - so continue polling mode for a while. */
+ vhost_disable_notify(vq->dev, vq);
+ vq->vqpoll.enabled = true;
+ vhost_enable_notify(vq->dev, vq);
+ return;
+ }
+ }
+
+ if (vq->vqpoll.avail_mapped) {
+ kunmap(vq->vqpoll.avail_page);
+ put_page(vq->vqpoll.avail_page);
+ vq->vqpoll.avail_mapped = 0;
+ }
+}
+
static void vhost_vq_reset(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
{
@@ -199,6 +288,48 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call = NULL;
vq->log_ctx = NULL;
vq->memory = NULL;
+ INIT_LIST_HEAD(&vq->vqpoll.link);
+ vq->vqpoll.enabled = false;
+ vq->vqpoll.shutdown = false;
+ vq->vqpoll.avail_mapped = NULL;
+}
+
+/* roundrobin_poll() takes worker->vqpoll_list, and returns one of the
+ * virtqueues which the caller should kick, or NULL in case none should be
+ * kicked. roundrobin_poll() also disables polling on a virtqueue which has
+ * been polled for too long without success.
+ *
+ * This current implementation (the "round-robin" implementation) only
+ * polls the first vq in the list, returning it or NULL as appropriate, and
+ * moves this vq to the end of the list, so next time a different one is
+ * polled.
+ */
+static struct vhost_virtqueue *roundrobin_poll(struct list_head *list)
+{
+ struct vhost_virtqueue *vq;
+ u16 avail_idx;
+
+ if (list_empty(list))
+ return NULL;
+
+ vq = list_first_entry(list, struct vhost_virtqueue, vqpoll.link);
+ WARN_ON(!vq->vqpoll.enabled);
+ list_move_tail(&vq->vqpoll.link, list);
+
+ /* See if there is any new work available from the guest. */
+ /* TODO: can check the optional idx feature, and if we haven't
+ * reached that idx yet, don't kick... */
+ avail_idx = vq->vqpoll.avail_mapped->idx;
+ if (avail_idx != vq->last_avail_idx)
+ return vq;
+
+ if (jiffies > vq->vqpoll.jiffies_last_kick + poll_stop_idle) {
+ /* We've been polling this virtqueue for a long time with no
+ * results, so switch back to guest notification
+ */
+ vhost_vq_disable_vqpoll(vq);
+ }
+ return NULL;
}
static int vhost_worker(void *data)
@@ -237,12 +368,62 @@ static int vhost_worker(void *data)
spin_unlock_irq(&dev->work_lock);
if (work) {
+ struct vhost_virtqueue *vq = work->vq;
__set_current_state(TASK_RUNNING);
work->fn(work);
+ /* Keep track of the work rate, for deciding when to
+ * enable polling */
+ if (vq) {
+ if (vq->vqpoll.jiffies_last_work != jiffies) {
+ vq->vqpoll.jiffies_last_work = jiffies;
+ vq->vqpoll.work_this_jiffy = 0;
+ }
+ vq->vqpoll.work_this_jiffy++;
+ }
+ /* If vq is in the round-robin list of virtqueues being
+ * constantly checked by this thread, move vq the end
+ * of the queue, because it had its fair chance now.
+ */
+ if (vq && !list_empty(&vq->vqpoll.link)) {
+ list_move_tail(&vq->vqpoll.link,
+ &dev->vqpoll_list);
+ }
+ /* Otherwise, if this vq is looking for notifications
+ * but vq polling is not enabled for it, do it now.
+ */
+ else if (poll_start_rate && vq && vq->handle_kick &&
+ !vq->vqpoll.enabled &&
+ !vq->vqpoll.shutdown &&
+ !(vq->used_flags & VRING_USED_F_NO_NOTIFY) &&
+ vq->vqpoll.work_this_jiffy >=
+ poll_start_rate) {
+ vhost_vq_enable_vqpoll(vq);
+ }
+ }
+ /* Check one virtqueue from the round-robin list */
+ if (!list_empty(&dev->vqpoll_list)) {
+ struct vhost_virtqueue *vq;
+
+ vq = roundrobin_poll(&dev->vqpoll_list);
+
+ if (vq) {
+ vq->handle_kick(&vq->poll.work);
+ vq->vqpoll.jiffies_last_kick = jiffies;
+ }
+
+ /* If our polling list isn't empty, ask to continue
+ * running this thread, don't yield.
+ */
+ __set_current_state(TASK_RUNNING);
if (need_resched())
schedule();
- } else
- schedule();
+ } else {
+ if (work) {
+ if (need_resched())
+ schedule();
+ } else
+ schedule();
+ }
}
unuse_mm(dev->mm);
@@ -306,6 +487,7 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->mm = NULL;
spin_lock_init(&dev->work_lock);
INIT_LIST_HEAD(&dev->work_list);
+ INIT_LIST_HEAD(&dev->vqpoll_list);
dev->worker = NULL;
for (i = 0; i < dev->nvqs; ++i) {
@@ -318,7 +500,7 @@ void vhost_dev_init(struct vhost_dev *dev,
vhost_vq_reset(dev, vq);
if (vq->handle_kick)
vhost_poll_init(&vq->poll, vq->handle_kick,
- POLLIN, dev);
+ POLLIN, vq);
}
}
EXPORT_SYMBOL_GPL(vhost_dev_init);
@@ -350,7 +532,7 @@ static int vhost_attach_cgroups(struct vhost_dev *dev)
struct vhost_attach_cgroups_struct attach;
attach.owner = current;
- vhost_work_init(&attach.work, vhost_attach_cgroups_work);
+ vhost_work_init(&attach.work, NULL, vhost_attach_cgroups_work);
vhost_work_queue(dev, &attach.work);
vhost_work_flush(dev, &attach.work);
return attach.ret;
@@ -444,6 +626,26 @@ void vhost_dev_stop(struct vhost_dev *dev)
}
EXPORT_SYMBOL_GPL(vhost_dev_stop);
+/* shutdown_vqpoll() asks the worker thread to shut down virtqueue polling
+ * mode for a given virtqueue which is itself being shut down. We ask the
+ * worker thread to do this rather than doing it directly, so that we don't
+ * race with the worker thread's use of the queue.
+ */
+static void shutdown_vqpoll_work(struct vhost_work *work)
+{
+ work->vq->vqpoll.shutdown = true;
+ vhost_vq_disable_vqpoll(work->vq);
+ WARN_ON(work->vq->vqpoll.avail_mapped);
+}
+
+static void shutdown_vqpoll(struct vhost_virtqueue *vq)
+{
+ struct vhost_work work;
+
+ vhost_work_init(&work, vq, shutdown_vqpoll_work);
+ vhost_work_queue(vq->dev, &work);
+ vhost_work_flush(vq->dev, &work);
+}
/* Caller should have device mutex if and only if locked is set */
void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
{
@@ -460,6 +662,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
eventfd_ctx_put(dev->vqs[i]->call_ctx);
if (dev->vqs[i]->call)
fput(dev->vqs[i]->call);
+ shutdown_vqpoll(dev->vqs[i]);
vhost_vq_reset(dev, dev->vqs[i]);
}
vhost_dev_free_iovecs(dev);
@@ -1491,6 +1694,19 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
u16 avail_idx;
int r;
+ /* In polling mode, when the backend (e.g., net.c) asks to enable
+ * notifications, we don't enable guest notifications. Instead, start
+ * polling on this vq by adding it to the round-robin list.
+ */
+ if (vq->vqpoll.enabled) {
+ if (list_empty(&vq->vqpoll.link)) {
+ list_add_tail(&vq->vqpoll.link,
+ &vq->dev->vqpoll_list);
+ vq->vqpoll.jiffies_last_kick = jiffies;
+ }
+ return false;
+ }
+
if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
return false;
vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
@@ -1528,6 +1744,17 @@ void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
int r;
+ /* If this virtqueue is vqpoll.enabled, and on the polling list, it
+ * will generate notifications even if the guest is asked not to send
+ * them. So we must remove it from the round-robin polling list.
+ * Note that vqpoll.enabled remains set.
+ */
+ if (vq->vqpoll.enabled) {
+ if (!list_empty(&vq->vqpoll.link))
+ list_del_init(&vq->vqpoll.link);
+ return;
+ }
+
if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
return;
vq->used_flags |= VRING_USED_F_NO_NOTIFY;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 3eda654..11aaaf4 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -24,6 +24,7 @@ struct vhost_work {
int flushing;
unsigned queue_seq;
unsigned done_seq;
+ struct vhost_virtqueue *vq;
};
/* Poll a file (eventfd or socket) */
@@ -37,11 +38,12 @@ struct vhost_poll {
struct vhost_dev *dev;
};
-void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);
+void vhost_work_init(struct vhost_work *work, struct vhost_virtqueue *vq,
+ vhost_work_fn_t fn);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
- unsigned long mask, struct vhost_dev *dev);
+ unsigned long mask, struct vhost_virtqueue *vq);
int vhost_poll_start(struct vhost_poll *poll, struct file *file);
void vhost_poll_stop(struct vhost_poll *poll);
void vhost_poll_flush(struct vhost_poll *poll);
@@ -54,8 +56,6 @@ struct vhost_log {
u64 len;
};
-struct vhost_virtqueue;
-
/* The virtqueue structure describes a queue attached to a device. */
struct vhost_virtqueue {
struct vhost_dev *dev;
@@ -110,6 +110,35 @@ struct vhost_virtqueue {
/* Log write descriptors */
void __user *log_base;
struct vhost_log *log;
+ struct {
+ /* When a virtqueue is in vqpoll.enabled mode, it declares
+ * that instead of using guest notifications (kicks) to
+ * discover new work, we prefer to continuously poll this
+ * virtqueue in the worker thread.
+ * If !enabled, the rest of the fields below are undefined.
+ */
+ bool enabled;
+ /* vqpoll.enabled doesn't always mean that this virtqueue is
+ * actually being polled: The backend (e.g., net.c) may
+ * temporarily disable it using vhost_disable/enable_notify().
+ * vqpoll.link is used to maintain the thread's round-robin
+ * list of virtqueues that actually need to be polled.
+ * Note list_empty(link) means this virtqueue isn't polled.
+ */
+ struct list_head link;
+ /* If this flag is true, the virtqueue is being shut down,
+ * so vqpoll should not be re-enabled.
+ */
+ bool shutdown;
+ /* Various counters used to decide when to enter polling mode
+ * or leave it and return to notification mode.
+ */
+ unsigned long jiffies_last_kick;
+ unsigned long jiffies_last_work;
+ int work_this_jiffy;
+ struct page *avail_page;
+ volatile struct vring_avail *avail_mapped;
+ } vqpoll;
};
struct vhost_dev {
@@ -123,6 +152,7 @@ struct vhost_dev {
spinlock_t work_lock;
struct list_head work_list;
struct task_struct *worker;
+ struct list_head vqpoll_list;
};
void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs, int nvqs);
--
1.7.9.5
^ permalink raw reply related [flat|nested] 2+ messages in thread