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    Subject[RFC v9 02/11] vhost: use batched get_vq_desc version
    Date
    From: "Michael S. Tsirkin" <mst@redhat.com>

    As testing shows no performance change, switch to that now.

    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
    Link: https://lore.kernel.org/r/20200401183118.8334-3-eperezma@redhat.com
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
    ---
    drivers/vhost/test.c | 2 +-
    drivers/vhost/vhost.c | 314 ++++++++----------------------------------
    drivers/vhost/vhost.h | 7 +-
    3 files changed, 61 insertions(+), 262 deletions(-)

    diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
    index a09dedc79f68..650e69261557 100644
    --- a/drivers/vhost/test.c
    +++ b/drivers/vhost/test.c
    @@ -119,7 +119,7 @@ static int vhost_test_open(struct inode *inode, struct file *f)
    dev = &n->dev;
    vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ];
    n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick;
    - vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV,
    + vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV + 64,
    VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT, true, NULL);

    f->private_data = n;
    diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
    index 2d784681b0fa..13021d6986eb 100644
    --- a/drivers/vhost/vhost.c
    +++ b/drivers/vhost/vhost.c
    @@ -304,6 +304,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
    {
    vq->num = 1;
    vq->ndescs = 0;
    + vq->first_desc = 0;
    vq->desc = NULL;
    vq->avail = NULL;
    vq->used = NULL;
    @@ -372,6 +373,11 @@ static int vhost_worker(void *data)
    return 0;
    }

    +static int vhost_vq_num_batch_descs(struct vhost_virtqueue *vq)
    +{
    + return vq->max_descs - UIO_MAXIOV;
    +}
    +
    static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
    {
    kfree(vq->descs);
    @@ -394,6 +400,9 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
    for (i = 0; i < dev->nvqs; ++i) {
    vq = dev->vqs[i];
    vq->max_descs = dev->iov_limit;
    + if (dev->use_worker && vhost_vq_num_batch_descs(vq) < 0) {
    + return -EINVAL;
    + }
    vq->descs = kmalloc_array(vq->max_descs,
    sizeof(*vq->descs),
    GFP_KERNEL);
    @@ -1610,6 +1619,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
    vq->last_avail_idx = s.num;
    /* Forget the cached index value. */
    vq->avail_idx = vq->last_avail_idx;
    + vq->ndescs = vq->first_desc = 0;
    break;
    case VHOST_GET_VRING_BASE:
    s.index = idx;
    @@ -2077,253 +2087,6 @@ static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc)
    return next;
    }

    -static int get_indirect(struct vhost_virtqueue *vq,
    - struct iovec iov[], unsigned int iov_size,
    - unsigned int *out_num, unsigned int *in_num,
    - struct vhost_log *log, unsigned int *log_num,
    - struct vring_desc *indirect)
    -{
    - struct vring_desc desc;
    - unsigned int i = 0, count, found = 0;
    - u32 len = vhost32_to_cpu(vq, indirect->len);
    - struct iov_iter from;
    - int ret, access;
    -
    - /* Sanity check */
    - if (unlikely(len % sizeof desc)) {
    - vq_err(vq, "Invalid length in indirect descriptor: "
    - "len 0x%llx not multiple of 0x%zx\n",
    - (unsigned long long)len,
    - sizeof desc);
    - return -EINVAL;
    - }
    -
    - ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect,
    - UIO_MAXIOV, VHOST_ACCESS_RO);
    - if (unlikely(ret < 0)) {
    - if (ret != -EAGAIN)
    - vq_err(vq, "Translation failure %d in indirect.\n", ret);
    - return ret;
    - }
    - iov_iter_init(&from, READ, vq->indirect, ret, len);
    -
    - /* We will use the result as an address to read from, so most
    - * architectures only need a compiler barrier here. */
    - read_barrier_depends();
    -
    - count = len / sizeof desc;
    - /* Buffers are chained via a 16 bit next field, so
    - * we can have at most 2^16 of these. */
    - if (unlikely(count > USHRT_MAX + 1)) {
    - vq_err(vq, "Indirect buffer length too big: %d\n",
    - indirect->len);
    - return -E2BIG;
    - }
    -
    - do {
    - unsigned iov_count = *in_num + *out_num;
    - if (unlikely(++found > count)) {
    - vq_err(vq, "Loop detected: last one at %u "
    - "indirect size %u\n",
    - i, count);
    - return -EINVAL;
    - }
    - if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) {
    - vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
    - i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
    - return -EINVAL;
    - }
    - if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) {
    - vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
    - i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
    - return -EINVAL;
    - }
    -
    - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
    - access = VHOST_ACCESS_WO;
    - else
    - access = VHOST_ACCESS_RO;
    -
    - ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
    - vhost32_to_cpu(vq, desc.len), iov + iov_count,
    - iov_size - iov_count, access);
    - if (unlikely(ret < 0)) {
    - if (ret != -EAGAIN)
    - vq_err(vq, "Translation failure %d indirect idx %d\n",
    - ret, i);
    - return ret;
    - }
    - /* If this is an input descriptor, increment that count. */
    - if (access == VHOST_ACCESS_WO) {
    - *in_num += ret;
    - if (unlikely(log && ret)) {
    - log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
    - log[*log_num].len = vhost32_to_cpu(vq, desc.len);
    - ++*log_num;
    - }
    - } else {
    - /* If it's an output descriptor, they're all supposed
    - * to come before any input descriptors. */
    - if (unlikely(*in_num)) {
    - vq_err(vq, "Indirect descriptor "
    - "has out after in: idx %d\n", i);
    - return -EINVAL;
    - }
    - *out_num += ret;
    - }
    - } while ((i = next_desc(vq, &desc)) != -1);
    - return 0;
    -}
    -
    -/* This looks in the virtqueue and for the first available buffer, and converts
    - * it to an iovec for convenient access. Since descriptors consist of some
    - * number of output then some number of input descriptors, it's actually two
    - * iovecs, but we pack them into one and note how many of each there were.
    - *
    - * This function returns the descriptor number found, or vq->num (which is
    - * never a valid descriptor number) if none was found. A negative code is
    - * returned on error. */
    -int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    - struct iovec iov[], unsigned int iov_size,
    - unsigned int *out_num, unsigned int *in_num,
    - struct vhost_log *log, unsigned int *log_num)
    -{
    - struct vring_desc desc;
    - unsigned int i, head, found = 0;
    - u16 last_avail_idx;
    - __virtio16 avail_idx;
    - __virtio16 ring_head;
    - int ret, access;
    -
    - /* Check it isn't doing very strange things with descriptor numbers. */
    - last_avail_idx = vq->last_avail_idx;
    -
    - if (vq->avail_idx == vq->last_avail_idx) {
    - if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
    - vq_err(vq, "Failed to access avail idx at %p\n",
    - &vq->avail->idx);
    - return -EFAULT;
    - }
    - vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
    -
    - if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
    - vq_err(vq, "Guest moved used index from %u to %u",
    - last_avail_idx, vq->avail_idx);
    - return -EFAULT;
    - }
    -
    - /* If there's nothing new since last we looked, return
    - * invalid.
    - */
    - if (vq->avail_idx == last_avail_idx)
    - return vq->num;
    -
    - /* Only get avail ring entries after they have been
    - * exposed by guest.
    - */
    - smp_rmb();
    - }
    -
    - /* Grab the next descriptor number they're advertising, and increment
    - * the index we've seen. */
    - if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
    - vq_err(vq, "Failed to read head: idx %d address %p\n",
    - last_avail_idx,
    - &vq->avail->ring[last_avail_idx % vq->num]);
    - return -EFAULT;
    - }
    -
    - head = vhost16_to_cpu(vq, ring_head);
    -
    - /* If their number is silly, that's an error. */
    - if (unlikely(head >= vq->num)) {
    - vq_err(vq, "Guest says index %u > %u is available",
    - head, vq->num);
    - return -EINVAL;
    - }
    -
    - /* When we start there are none of either input nor output. */
    - *out_num = *in_num = 0;
    - if (unlikely(log))
    - *log_num = 0;
    -
    - i = head;
    - do {
    - unsigned iov_count = *in_num + *out_num;
    - if (unlikely(i >= vq->num)) {
    - vq_err(vq, "Desc index is %u > %u, head = %u",
    - i, vq->num, head);
    - return -EINVAL;
    - }
    - if (unlikely(++found > vq->num)) {
    - vq_err(vq, "Loop detected: last one at %u "
    - "vq size %u head %u\n",
    - i, vq->num, head);
    - return -EINVAL;
    - }
    - ret = vhost_get_desc(vq, &desc, i);
    - if (unlikely(ret)) {
    - vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
    - i, vq->desc + i);
    - return -EFAULT;
    - }
    - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) {
    - ret = get_indirect(vq, iov, iov_size,
    - out_num, in_num,
    - log, log_num, &desc);
    - if (unlikely(ret < 0)) {
    - if (ret != -EAGAIN)
    - vq_err(vq, "Failure detected "
    - "in indirect descriptor at idx %d\n", i);
    - return ret;
    - }
    - continue;
    - }
    -
    - if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
    - access = VHOST_ACCESS_WO;
    - else
    - access = VHOST_ACCESS_RO;
    - ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
    - vhost32_to_cpu(vq, desc.len), iov + iov_count,
    - iov_size - iov_count, access);
    - if (unlikely(ret < 0)) {
    - if (ret != -EAGAIN)
    - vq_err(vq, "Translation failure %d descriptor idx %d\n",
    - ret, i);
    - return ret;
    - }
    - if (access == VHOST_ACCESS_WO) {
    - /* If this is an input descriptor,
    - * increment that count. */
    - *in_num += ret;
    - if (unlikely(log && ret)) {
    - log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
    - log[*log_num].len = vhost32_to_cpu(vq, desc.len);
    - ++*log_num;
    - }
    - } else {
    - /* If it's an output descriptor, they're all supposed
    - * to come before any input descriptors. */
    - if (unlikely(*in_num)) {
    - vq_err(vq, "Descriptor has out after in: "
    - "idx %d\n", i);
    - return -EINVAL;
    - }
    - *out_num += ret;
    - }
    - } while ((i = next_desc(vq, &desc)) != -1);
    -
    - /* On success, increment avail index. */
    - vq->last_avail_idx++;
    -
    - /* Assume notifications from guest are disabled at this point,
    - * if they aren't we would need to update avail_event index. */
    - BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
    - return head;
    -}
    -EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
    -
    static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq)
    {
    BUG_ON(!vq->ndescs);
    @@ -2427,7 +2190,7 @@ static int fetch_indirect_descs(struct vhost_virtqueue *vq,

    /* This function returns a value > 0 if a descriptor was found, or 0 if none were found.
    * A negative code is returned on error. */
    -static int fetch_descs(struct vhost_virtqueue *vq)
    +static int fetch_buf(struct vhost_virtqueue *vq)
    {
    unsigned int i, head, found = 0;
    struct vhost_desc *last;
    @@ -2440,7 +2203,7 @@ static int fetch_descs(struct vhost_virtqueue *vq)
    /* Check it isn't doing very strange things with descriptor numbers. */
    last_avail_idx = vq->last_avail_idx;

    - if (vq->avail_idx == vq->last_avail_idx) {
    + if (unlikely(vq->avail_idx == vq->last_avail_idx)) {
    if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
    vq_err(vq, "Failed to access avail idx at %p\n",
    &vq->avail->idx);
    @@ -2531,6 +2294,41 @@ static int fetch_descs(struct vhost_virtqueue *vq)
    return 1;
    }

    +/* This function returns a value > 0 if a descriptor was found, or 0 if none were found.
    + * A negative code is returned on error. */
    +static int fetch_descs(struct vhost_virtqueue *vq)
    +{
    + int ret;
    +
    + if (unlikely(vq->first_desc >= vq->ndescs)) {
    + vq->first_desc = 0;
    + vq->ndescs = 0;
    + }
    +
    + if (vq->ndescs)
    + return 1;
    +
    + for (ret = 1;
    + ret > 0 && vq->ndescs <= vhost_vq_num_batch_descs(vq);
    + ret = fetch_buf(vq))
    + ;
    +
    + /* On success we expect some descs */
    + BUG_ON(ret > 0 && !vq->ndescs);
    + return vq->ndescs ? vq->ndescs : ret;
    +}
    +
    +/* Reverse the effects of fetch_descs */
    +static void unfetch_descs(struct vhost_virtqueue *vq)
    +{
    + int i;
    +
    + for (i = vq->first_desc; i < vq->ndescs; ++i)
    + if (!(vq->descs[i].flags & VRING_DESC_F_NEXT))
    + vq->last_avail_idx -= 1;
    + vq->ndescs = 0;
    +}
    +
    /* This looks in the virtqueue and for the first available buffer, and converts
    * it to an iovec for convenient access. Since descriptors consist of some
    * number of output then some number of input descriptors, it's actually two
    @@ -2539,7 +2337,7 @@ static int fetch_descs(struct vhost_virtqueue *vq)
    * This function returns the descriptor number found, or vq->num (which is
    * never a valid descriptor number) if none was found. A negative code is
    * returned on error. */
    -int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
    +int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    struct iovec iov[], unsigned int iov_size,
    unsigned int *out_num, unsigned int *in_num,
    struct vhost_log *log, unsigned int *log_num)
    @@ -2548,7 +2346,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
    int i;

    if (ret <= 0)
    - goto err_fetch;
    + goto err;

    /* Now convert to IOV */
    /* When we start there are none of either input nor output. */
    @@ -2556,7 +2354,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
    if (unlikely(log))
    *log_num = 0;

    - for (i = 0; i < vq->ndescs; ++i) {
    + for (i = vq->first_desc; i < vq->ndescs; ++i) {
    unsigned iov_count = *in_num + *out_num;
    struct vhost_desc *desc = &vq->descs[i];
    int access;
    @@ -2602,24 +2400,26 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
    }

    ret = desc->id;
    +
    + if (!(desc->flags & VRING_DESC_F_NEXT))
    + break;
    }

    - vq->ndescs = 0;
    + vq->first_desc = i + 1;

    return ret;

    err:
    - vhost_discard_vq_desc(vq, 1);
    -err_fetch:
    - vq->ndescs = 0;
    + unfetch_descs(vq);

    return ret ? ret : vq->num;
    }
    -EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch);
    +EXPORT_SYMBOL_GPL(vhost_get_vq_desc);

    /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
    void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
    {
    + unfetch_descs(vq);
    vq->last_avail_idx -= n;
    }
    EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
    diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
    index 87089d51490d..fed36af5c444 100644
    --- a/drivers/vhost/vhost.h
    +++ b/drivers/vhost/vhost.h
    @@ -81,6 +81,7 @@ struct vhost_virtqueue {

    struct vhost_desc *descs;
    int ndescs;
    + int first_desc;
    int max_descs;

    struct file *kick;
    @@ -189,10 +190,6 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
    bool vhost_vq_access_ok(struct vhost_virtqueue *vq);
    bool vhost_log_access_ok(struct vhost_dev *);

    -int vhost_get_vq_desc_batch(struct vhost_virtqueue *,
    - struct iovec iov[], unsigned int iov_count,
    - unsigned int *out_num, unsigned int *in_num,
    - struct vhost_log *log, unsigned int *log_num);
    int vhost_get_vq_desc(struct vhost_virtqueue *,
    struct iovec iov[], unsigned int iov_count,
    unsigned int *out_num, unsigned int *in_num,
    @@ -261,6 +258,8 @@ static inline void vhost_vq_set_backend(struct vhost_virtqueue *vq,
    void *private_data)
    {
    vq->private_data = private_data;
    + vq->ndescs = 0;
    + vq->first_desc = 0;
    }

    /**
    --
    2.18.1
    \
     
     \ /
      Last update: 2020-06-19 20:26    [W:9.078 / U:0.052 seconds]
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