Messages in this thread | | | Subject | Re: [PATCH RFC 03/13] vhost: batching fetches | From | Jason Wang <> | Date | Mon, 8 Jun 2020 11:35:40 +0800 |
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On 2020/6/7 下午9:57, Michael S. Tsirkin wrote: > On Fri, Jun 05, 2020 at 11:40:17AM +0800, Jason Wang wrote: >> On 2020/6/4 下午4:59, Michael S. Tsirkin wrote: >>> On Wed, Jun 03, 2020 at 03:27:39PM +0800, Jason Wang wrote: >>>> On 2020/6/2 下午9:06, Michael S. Tsirkin wrote: >>>>> With this patch applied, new and old code perform identically. >>>>> >>>>> Lots of extra optimizations are now possible, e.g. >>>>> we can fetch multiple heads with copy_from/to_user now. >>>>> We can get rid of maintaining the log array. Etc etc. >>>>> >>>>> Signed-off-by: Michael S. Tsirkin<mst@redhat.com> >>>>> Signed-off-by: Eugenio Pérez<eperezma@redhat.com> >>>>> Link:https://lore.kernel.org/r/20200401183118.8334-4-eperezma@redhat.com >>>>> Signed-off-by: Michael S. Tsirkin<mst@redhat.com> >>>>> --- >>>>> drivers/vhost/test.c | 2 +- >>>>> drivers/vhost/vhost.c | 47 ++++++++++++++++++++++++++++++++++++++----- >>>>> drivers/vhost/vhost.h | 5 ++++- >>>>> 3 files changed, 47 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c >>>>> index 9a3a09005e03..02806d6f84ef 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, NULL); >>>>> f->private_data = n; >>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >>>>> index 8f9a07282625..aca2a5b0d078 100644 >>>>> --- a/drivers/vhost/vhost.c >>>>> +++ b/drivers/vhost/vhost.c >>>>> @@ -299,6 +299,7 @@ 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; >>>>> @@ -367,6 +368,11 @@ 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; >>>>> +} >>>> 1 descriptor does not mean 1 iov, e.g userspace may pass several 1 byte >>>> length memory regions for us to translate. >>>> >>> Yes but I don't see the relevance. This tells us how many descriptors to >>> batch, not how many IOVs. >> Yes, but questions are: >> >> - this introduce another obstacle to support more than 1K queue size >> - if we support 1K queue size, does it mean we need to cache 1K descriptors, >> which seems a large stress on the cache >> >> Thanks >> >> > Still don't understand the relevance. We support up to 1K descriptors > per buffer just for IOV since we always did. This adds 64 more > descriptors - is that a big deal?
If I understanding correctly, for net, the code tries to batch descriptors for at last one packet.
If we allow 1K queue size then we allow a packet that consists of 1K descriptors. Then we need to cache 1K descriptors.
Thanks
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