From 7b21e34fd1c272e3a8c3846168f2f6287a4cd72b Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Thu, 12 Jan 2012 15:44:42 +1030 Subject: [PATCH] virtio: harsher barriers for rpmsg. We were cheating with our barriers; using the smp ones rather than the real device ones. That was fine, until rpmsg came along, which is used to talk to a real device (a non-SMP CPU). Unfortunately, just putting back the real barriers (reverting d57ed95d) causes a performance regression on virtio-pci. In particular, Amos reports netbench's TCP_RR over virtio_net CPU utilization increased up to 35% while throughput went down by up to 14%. By comparison, this branch is in the noise. Reference: https://lkml.org/lkml/2011/12/11/22 Signed-off-by: Rusty Russell --- drivers/lguest/lguest_device.c | 8 +++++--- drivers/s390/kvm/kvm_virtio.c | 2 +- drivers/virtio/virtio_mmio.c | 4 ++-- drivers/virtio/virtio_pci.c | 4 ++-- drivers/virtio/virtio_ring.c | 34 +++++++++++++++++++++------------- include/linux/virtio_ring.h | 1 + tools/virtio/linux/virtio.h | 1 + tools/virtio/virtio_test.c | 3 ++- 8 files changed, 35 insertions(+), 22 deletions(-) diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c index 595d7319701..6a1d6447b86 100644 --- a/drivers/lguest/lguest_device.c +++ b/drivers/lguest/lguest_device.c @@ -292,10 +292,12 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev, /* * OK, tell virtio_ring.c to set up a virtqueue now we know its size - * and we've got a pointer to its pages. + * and we've got a pointer to its pages. Note that we set weak_barriers + * to 'true': the host just a(nother) SMP CPU, so we only need inter-cpu + * barriers. */ - vq = vring_new_virtqueue(lvq->config.num, LGUEST_VRING_ALIGN, - vdev, lvq->pages, lg_notify, callback, name); + vq = vring_new_virtqueue(lvq->config.num, LGUEST_VRING_ALIGN, vdev, + true, lvq->pages, lg_notify, callback, name); if (!vq) { err = -ENOMEM; goto unmap; diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c index 8af868bab20..7bc1955337e 100644 --- a/drivers/s390/kvm/kvm_virtio.c +++ b/drivers/s390/kvm/kvm_virtio.c @@ -198,7 +198,7 @@ static struct virtqueue *kvm_find_vq(struct virtio_device *vdev, goto out; vq = vring_new_virtqueue(config->num, KVM_S390_VIRTIO_RING_ALIGN, - vdev, (void *) config->address, + vdev, true, (void *) config->address, kvm_notify, callback, name); if (!vq) { err = -ENOMEM; diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c index 0269717436a..01d6dc250d5 100644 --- a/drivers/virtio/virtio_mmio.c +++ b/drivers/virtio/virtio_mmio.c @@ -310,8 +310,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN); /* Create the vring */ - vq = vring_new_virtqueue(info->num, VIRTIO_MMIO_VRING_ALIGN, - vdev, info->queue, vm_notify, callback, name); + vq = vring_new_virtqueue(info->num, VIRTIO_MMIO_VRING_ALIGN, vdev, + true, info->queue, vm_notify, callback, name); if (!vq) { err = -ENOMEM; goto error_new_virtqueue; diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c index baabb7937ec..688b42d28da 100644 --- a/drivers/virtio/virtio_pci.c +++ b/drivers/virtio/virtio_pci.c @@ -414,8 +414,8 @@ static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN); /* create the vring */ - vq = vring_new_virtqueue(info->num, VIRTIO_PCI_VRING_ALIGN, - vdev, info->queue, vp_notify, callback, name); + vq = vring_new_virtqueue(info->num, VIRTIO_PCI_VRING_ALIGN, vdev, + true, info->queue, vp_notify, callback, name); if (!vq) { err = -ENOMEM; goto out_activate_queue; diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index c7a2c208f6e..50da9204609 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -28,17 +28,20 @@ #ifdef CONFIG_SMP /* Where possible, use SMP barriers which are more lightweight than mandatory * barriers, because mandatory barriers control MMIO effects on accesses - * through relaxed memory I/O windows (which virtio does not use). */ -#define virtio_mb() smp_mb() -#define virtio_rmb() smp_rmb() -#define virtio_wmb() smp_wmb() + * through relaxed memory I/O windows (which virtio-pci does not use). */ +#define virtio_mb(vq) \ + do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0) +#define virtio_rmb(vq) \ + do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0) +#define virtio_wmb(vq) \ + do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0) #else /* We must force memory ordering even if guest is UP since host could be * running on another CPU, but SMP barriers are defined to barrier() in that * configuration. So fall back to mandatory barriers instead. */ -#define virtio_mb() mb() -#define virtio_rmb() rmb() -#define virtio_wmb() wmb() +#define virtio_mb(vq) mb() +#define virtio_rmb(vq) rmb() +#define virtio_wmb(vq) wmb() #endif #ifdef DEBUG @@ -77,6 +80,9 @@ struct vring_virtqueue /* Actual memory layout for this queue */ struct vring vring; + /* Can we use weak barriers? */ + bool weak_barriers; + /* Other side has made a mess, don't try any more. */ bool broken; @@ -245,14 +251,14 @@ void virtqueue_kick(struct virtqueue *_vq) START_USE(vq); /* Descriptors and available array need to be set before we expose the * new available array entries. */ - virtio_wmb(); + virtio_wmb(vq); old = vq->vring.avail->idx; new = vq->vring.avail->idx = old + vq->num_added; vq->num_added = 0; /* Need to update avail index before checking if we should notify */ - virtio_mb(); + virtio_mb(vq); if (vq->event ? vring_need_event(vring_avail_event(&vq->vring), new, old) : @@ -314,7 +320,7 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) } /* Only get used array entries after they have been exposed by host. */ - virtio_rmb(); + virtio_rmb(vq); i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id; *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len; @@ -337,7 +343,7 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) * the read in the next get_buf call. */ if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) { vring_used_event(&vq->vring) = vq->last_used_idx; - virtio_mb(); + virtio_mb(vq); } END_USE(vq); @@ -366,7 +372,7 @@ bool virtqueue_enable_cb(struct virtqueue *_vq) * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; vring_used_event(&vq->vring) = vq->last_used_idx; - virtio_mb(); + virtio_mb(vq); if (unlikely(more_used(vq))) { END_USE(vq); return false; @@ -393,7 +399,7 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) /* TODO: tune this threshold */ bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4; vring_used_event(&vq->vring) = vq->last_used_idx + bufs; - virtio_mb(); + virtio_mb(vq); if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) { END_USE(vq); return false; @@ -453,6 +459,7 @@ EXPORT_SYMBOL_GPL(vring_interrupt); struct virtqueue *vring_new_virtqueue(unsigned int num, unsigned int vring_align, struct virtio_device *vdev, + bool weak_barriers, void *pages, void (*notify)(struct virtqueue *), void (*callback)(struct virtqueue *), @@ -476,6 +483,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num, vq->vq.vdev = vdev; vq->vq.name = name; vq->notify = notify; + vq->weak_barriers = weak_barriers; vq->broken = false; vq->last_used_idx = 0; vq->num_added = 0; diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 36be0f6e18a..e338730c266 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -168,6 +168,7 @@ struct virtqueue; struct virtqueue *vring_new_virtqueue(unsigned int num, unsigned int vring_align, struct virtio_device *vdev, + bool weak_barriers, void *pages, void (*notify)(struct virtqueue *vq), void (*callback)(struct virtqueue *vq), diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h index 669bcdd4580..953db2abf6b 100644 --- a/tools/virtio/linux/virtio.h +++ b/tools/virtio/linux/virtio.h @@ -214,6 +214,7 @@ void *virtqueue_detach_unused_buf(struct virtqueue *vq); struct virtqueue *vring_new_virtqueue(unsigned int num, unsigned int vring_align, struct virtio_device *vdev, + bool weak_barriers, void *pages, void (*notify)(struct virtqueue *vq), void (*callback)(struct virtqueue *vq), diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c index 74d3331bdaf..0740284396c 100644 --- a/tools/virtio/virtio_test.c +++ b/tools/virtio/virtio_test.c @@ -92,7 +92,8 @@ static void vq_info_add(struct vdev_info *dev, int num) assert(r >= 0); memset(info->ring, 0, vring_size(num, 4096)); vring_init(&info->vring, num, info->ring, 4096); - info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev, info->ring, + info->vq = vring_new_virtqueue(info->vring.num, 4096, &dev->vdev, + true, info->ring, vq_notify, vq_callback, "test"); assert(info->vq); info->vq->priv = info; -- 2.20.1