[dpdk-dev] [PATCH v5] vhost_user: protect active rings from async ring changes
Chen, Junjie J
junjie.j.chen at intel.com
Wed Jan 31 09:42:34 CET 2018
Make sense, Thanks.
Cheers
JJ
> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
> Sent: Wednesday, January 31, 2018 4:13 PM
> To: Chen, Junjie J <junjie.j.chen at intel.com>; Victor Kaplansky
> <victork at redhat.com>
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v5] vhost_user: protect active rings from
> async ring changes
>
> Hi,
>
> On 01/31/2018 07:51 AM, Chen, Junjie J wrote:
> > Hi
> > May I know why not use trylock also in enqueue path?
>
> Because if rte_vhost_enqueue_burst() returns 0, the caller is likely to drop
> the packets. This is what happens for example with OVS:
>
> static void
> __netdev_dpdk_vhost_send(struct netdev *netdev, int qid,
> struct dp_packet **pkts, int cnt) { ...
> do {
> int vhost_qid = qid * VIRTIO_QNUM + VIRTIO_RXQ;
> unsigned int tx_pkts;
>
> tx_pkts = rte_vhost_enqueue_burst(vid, vhost_qid, cur_pkts, cnt);
> if (OVS_LIKELY(tx_pkts)) {
> /* Packets have been sent.*/
> cnt -= tx_pkts;
> /* Prepare for possible retry.*/
> cur_pkts = &cur_pkts[tx_pkts];
> } else {
> /* No packets sent - do not retry.*/
> break;
> }
> } while (cnt && (retries++ <= VHOST_ENQ_RETRY_NUM)); ...
>
>
> Maxime
> > Cheers
> > JJ
> >
> >>
> >> When performing live migration or memory hot-plugging, the changes to
> >> the device and vrings made by message handler done independently from
> >> vring usage by PMD threads.
> >>
> >> This causes for example segfaults during live-migration with MQ
> >> enable, but in general virtually any request sent by qemu changing
> >> the state of device can cause problems.
> >>
> >> These patches fixes all above issues by adding a spinlock to every
> >> vring and requiring message handler to start operation only after
> >> ensuring that all PMD threads related to the device are out of
> >> critical section accessing the vring data.
> >>
> >> Each vring has its own lock in order to not create contention between
> >> PMD threads of different vrings and to prevent performance
> >> degradation by scaling queue pair number.
> >>
> >> See https://bugzilla.redhat.com/show_bug.cgi?id=1450680
> >>
> >> Signed-off-by: Victor Kaplansky <victork at redhat.com>
> >> ---
> >> v5:
> >> o get rid of spinlock wrapping functions in vhost.h
> >>
> >> v4:
> >>
> >> o moved access_unlock before accessing enable flag and
> >> access_unlock after iommu_unlock consistently.
> >> o cosmetics: removed blank line.
> >> o the access_lock variable moved to be in the same
> >> cache line with enable and access_ok flags.
> >> o dequeue path is now guarded with trylock and returning
> >> zero if unsuccessful.
> >> o GET_VRING_BASE operation is not guarded by access lock
> >> to avoid deadlock with device_destroy. See the comment
> >> in the code.
> >> o Fixed error path exit from enqueue and dequeue carefully
> >> unlocking access and iommu locks as appropriate.
> >>
> >> v3:
> >> o Added locking to enqueue flow.
> >> o Enqueue path guarded as well as dequeue path.
> >> o Changed name of active_lock.
> >> o Added initialization of guarding spinlock.
> >> o Reworked functions skimming over all virt-queues.
> >> o Performance measurements done by Maxime Coquelin shows
> >> no degradation in bandwidth and throughput.
> >> o Spelling.
> >> o Taking lock only on set operations.
> >> o IOMMU messages are not guarded by access lock.
> >>
> >> v2:
> >> o Fixed checkpatch complains.
> >> o Added Signed-off-by.
> >> o Refined placement of guard to exclude IOMMU messages.
> >> o TODO: performance degradation measurement.
> >>
> >> lib/librte_vhost/vhost.h | 6 ++--
> >> lib/librte_vhost/vhost.c | 1 +
> >> lib/librte_vhost/vhost_user.c | 70
> >> +++++++++++++++++++++++++++++++++++++++++++
> >> lib/librte_vhost/virtio_net.c | 28 ++++++++++++++---
> >> 4 files changed, 99 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> >> index
> >> 1cc81c17..c8f2a817 100644
> >> --- a/lib/librte_vhost/vhost.h
> >> +++ b/lib/librte_vhost/vhost.h
> >> @@ -108,12 +108,14 @@ struct vhost_virtqueue {
> >>
> >> /* Backend value to determine if device should started/stopped */
> >> int backend;
> >> + int enabled;
> >> + int access_ok;
> >> + rte_spinlock_t access_lock;
> >> +
> >> /* Used to notify the guest (trigger interrupt) */
> >> int callfd;
> >> /* Currently unused as polling mode is enabled */
> >> int kickfd;
> >> - int enabled;
> >> - int access_ok;
> >>
> >> /* Physical address of used ring, for logging */
> >> uint64_t log_guest_addr;
> >> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> >> index
> >> 4f8b73a0..dcc42fc7 100644
> >> --- a/lib/librte_vhost/vhost.c
> >> +++ b/lib/librte_vhost/vhost.c
> >> @@ -259,6 +259,7 @@ alloc_vring_queue(struct virtio_net *dev,
> >> uint32_t
> >> vring_idx)
> >>
> >> dev->virtqueue[vring_idx] = vq;
> >> init_vring_queue(dev, vring_idx);
> >> + rte_spinlock_init(&vq->access_lock);
> >>
> >> dev->nr_vring += 1;
> >>
> >> diff --git a/lib/librte_vhost/vhost_user.c
> >> b/lib/librte_vhost/vhost_user.c index f4c7ce46..0685d4e7 100644
> >> --- a/lib/librte_vhost/vhost_user.c
> >> +++ b/lib/librte_vhost/vhost_user.c
> >> @@ -1190,12 +1190,47 @@
> >> vhost_user_check_and_alloc_queue_pair(struct virtio_net *dev,
> >> VhostUserMsg *msg)
> >> return alloc_vring_queue(dev, vring_idx); }
> >>
> >> +static void
> >> +vhost_user_lock_all_queue_pairs(struct virtio_net *dev) {
> >> + unsigned int i = 0;
> >> + unsigned int vq_num = 0;
> >> +
> >> + while (vq_num < dev->nr_vring) {
> >> + struct vhost_virtqueue *vq = dev->virtqueue[i];
> >> +
> >> + if (vq) {
> >> + rte_spinlock_lock(&vq->access_lock);
> >> + vq_num++;
> >> + }
> >> + i++;
> >> + }
> >> +}
> >> +
> >> +static void
> >> +vhost_user_unlock_all_queue_pairs(struct virtio_net *dev) {
> >> + unsigned int i = 0;
> >> + unsigned int vq_num = 0;
> >> +
> >> + while (vq_num < dev->nr_vring) {
> >> + struct vhost_virtqueue *vq = dev->virtqueue[i];
> >> +
> >> + if (vq) {
> >> + rte_spinlock_unlock(&vq->access_lock);
> >> + vq_num++;
> >> + }
> >> + i++;
> >> + }
> >> +}
> >> +
> >> int
> >> vhost_user_msg_handler(int vid, int fd) {
> >> struct virtio_net *dev;
> >> struct VhostUserMsg msg;
> >> int ret;
> >> + int unlock_required = 0;
> >>
> >> dev = get_device(vid);
> >> if (dev == NULL)
> >> @@ -1241,6 +1276,38 @@ vhost_user_msg_handler(int vid, int fd)
> >> return -1;
> >> }
> >>
> >> + /*
> >> + * Note: we don't lock all queues on VHOST_USER_GET_VRING_BASE,
> >> + * since it is sent when virtio stops and device is destroyed.
> >> + * destroy_device waits for queues to be inactive, so it is safe.
> >> + * Otherwise taking the access_lock would cause a dead lock.
> >> + */
> >> + switch (msg.request.master) {
> >> + case VHOST_USER_SET_FEATURES:
> >> + case VHOST_USER_SET_PROTOCOL_FEATURES:
> >> + case VHOST_USER_SET_OWNER:
> >> + case VHOST_USER_RESET_OWNER:
> >> + case VHOST_USER_SET_MEM_TABLE:
> >> + case VHOST_USER_SET_LOG_BASE:
> >> + case VHOST_USER_SET_LOG_FD:
> >> + case VHOST_USER_SET_VRING_NUM:
> >> + case VHOST_USER_SET_VRING_ADDR:
> >> + case VHOST_USER_SET_VRING_BASE:
> >> + case VHOST_USER_SET_VRING_KICK:
> >> + case VHOST_USER_SET_VRING_CALL:
> >> + case VHOST_USER_SET_VRING_ERR:
> >> + case VHOST_USER_SET_VRING_ENABLE:
> >> + case VHOST_USER_SEND_RARP:
> >> + case VHOST_USER_NET_SET_MTU:
> >> + case VHOST_USER_SET_SLAVE_REQ_FD:
> >> + vhost_user_lock_all_queue_pairs(dev);
> >> + unlock_required = 1;
> >> + break;
> >> + default:
> >> + break;
> >> +
> >> + }
> >> +
> >> switch (msg.request.master) {
> >> case VHOST_USER_GET_FEATURES:
> >> msg.payload.u64 = vhost_user_get_features(dev); @@
> -1342,6
> >> +1409,9 @@ vhost_user_msg_handler(int vid, int fd)
> >>
> >> }
> >>
> >> + if (unlock_required)
> >> + vhost_user_unlock_all_queue_pairs(dev);
> >> +
> >> if (msg.flags & VHOST_USER_NEED_REPLY) {
> >> msg.payload.u64 = !!ret;
> >> msg.size = sizeof(msg.payload.u64); diff --git
> >> a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index
> >> 6fee16e5..e09a927d 100644
> >> --- a/lib/librte_vhost/virtio_net.c
> >> +++ b/lib/librte_vhost/virtio_net.c
> >> @@ -44,6 +44,7 @@
> >> #include <rte_udp.h>
> >> #include <rte_sctp.h>
> >> #include <rte_arp.h>
> >> +#include <rte_spinlock.h>
> >>
> >> #include "iotlb.h"
> >> #include "vhost.h"
> >> @@ -326,8 +327,11 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t
> >> queue_id,
> >> }
> >>
> >> vq = dev->virtqueue[queue_id];
> >> +
> >> + rte_spinlock_lock(&vq->access_lock);
> >> +
> >> if (unlikely(vq->enabled == 0))
> >> - return 0;
> >> + goto out_access_unlock;
> >>
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >> vhost_user_iotlb_rd_lock(vq);
> >> @@ -419,6 +423,9 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t
> >> queue_id,
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >> vhost_user_iotlb_rd_unlock(vq);
> >>
> >> +out_access_unlock:
> >> + rte_spinlock_unlock(&vq->access_lock);
> >> +
> >> return count;
> >> }
> >>
> >> @@ -651,8 +658,11 @@ virtio_dev_merge_rx(struct virtio_net *dev,
> >> uint16_t queue_id,
> >> }
> >>
> >> vq = dev->virtqueue[queue_id];
> >> +
> >> + rte_spinlock_lock(&vq->access_lock);
> >> +
> >> if (unlikely(vq->enabled == 0))
> >> - return 0;
> >> + goto out_access_unlock;
> >>
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >> vhost_user_iotlb_rd_lock(vq);
> >> @@ -715,6 +725,9 @@ virtio_dev_merge_rx(struct virtio_net *dev,
> >> uint16_t queue_id,
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >> vhost_user_iotlb_rd_unlock(vq);
> >>
> >> +out_access_unlock:
> >> + rte_spinlock_unlock(&vq->access_lock);
> >> +
> >> return pkt_idx;
> >> }
> >>
> >> @@ -1180,9 +1193,13 @@ rte_vhost_dequeue_burst(int vid, uint16_t
> >> queue_id,
> >> }
> >>
> >> vq = dev->virtqueue[queue_id];
> >> - if (unlikely(vq->enabled == 0))
> >> +
> >> + if (unlikely(rte_spinlock_trylock(&vq->access_lock) == 0))
> >> return 0;
> >>
> >> + if (unlikely(vq->enabled == 0))
> >> + goto out_access_unlock;
> >> +
> >> vq->batch_copy_nb_elems = 0;
> >>
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)) @@
> >> -1240,7 +1257,7 @@ rte_vhost_dequeue_burst(int vid, uint16_t
> queue_id,
> >> if (rarp_mbuf == NULL) {
> >> RTE_LOG(ERR, VHOST_DATA,
> >> "Failed to allocate memory for mbuf.\n");
> >> - return 0;
> >> + goto out;
> >> }
> >>
> >> if (make_rarp_packet(rarp_mbuf, &dev->mac)) { @@ -1356,6
> >> +1373,9 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
> >> if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >> vhost_user_iotlb_rd_unlock(vq);
> >>
> >> +out_access_unlock:
> >> + rte_spinlock_unlock(&vq->access_lock);
> >> +
> >> if (unlikely(rarp_mbuf != NULL)) {
> >> /*
> >> * Inject it to the head of "pkts" array, so that switch's mac
> >> --
> >> Victor
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