Messages in this thread | | On 06/21/2017 08:28 PM, Michael S. Tsirkin wrote: > On Wed, Jun 21, 2017 at 11:28:00AM +0800, Wei Wang wrote: >> On 06/21/2017 12:18 AM, Michael S. Tsirkin wrote: >>> On Fri, Jun 09, 2017 at 06:41:41PM +0800, Wei Wang wrote: >>>> - if (!virtqueue_indirect_desc_table_add(vq, desc, num)) { >>>> + if (!virtqueue_indirect_desc_table_add(vq, desc, *num)) { >>>> virtqueue_kick(vq); >>>> - wait_event(vb->acked, virtqueue_get_buf(vq, &len)); >>>> - vb->balloon_page_chunk.chunk_num = 0; >>>> + if (busy_wait) >>>> + while (!virtqueue_get_buf(vq, &len) && >>>> + !virtqueue_is_broken(vq)) >>>> + cpu_relax(); >>>> + else >>>> + wait_event(vb->acked, virtqueue_get_buf(vq, &len)); >>> This is something I didn't previously notice. >>> As you always keep a single buffer in flight, you do not >>> really need indirect at all. Just add all descriptors >>> in the ring directly, then kick. >>> >>> E.g. >>> virtqueue_add_first >>> virtqueue_add_next >>> virtqueue_add_last >>> >>> ? >>> >>> You also want a flag to avoid allocations but there's no need to do it >>> per descriptor, set it on vq. >>> >> Without using the indirect table, I'm thinking about changing to use >> the standard sg (i.e. struct scatterlist), instead of vring_desc, so that >> we don't need to modify or add any new functions of virtqueue_add(). >> >> In this case, we will kmalloc an array of sgs in probe(), and we can add >> the sgs one by one to the vq, which won't trigger the allocation of an >> indirect table inside virtqueue_add(), and then kick when all are added. >> >> Best, >> Wei > And allocate headers too? This can work. API extensions aren't > necessarily a bad idea though. The API I suggest above is preferable > for the simple reason that it can work without INDIRECT flag > support in hypervisor.
OK, probably we don't need to add a desc to the vq - we can just use the vq's desc, like this:
int virtqueue_add_first(struct virtqueue *_vq, uint64_t addr, uint32_t len, bool in, unsigned int *idx) {
... uint16_t desc_flags = in ? VRING_DESC_F_NEXT | VRING_DESC_F_WRITE : VRING_DESC_F_NEXT;
vq->vring.desc[vq->free_head].addr = addr; vq->vring.desc[vq->free_head].len = len; vq->vring.desc[vq->free_head].flags = cpu_to_virtio16(_vq->vdev, flags); /* return to the caller the desc id */ *idx = vq->free_head; ... }
int virtqueue_add_next(struct virtqueue *_vq, uint64_t addr, uint32_t len, bool in, bool end, unsigned int *idx) { ... vq->vring.desc[*idx].next = vq->free_head; vq->vring.desc[vq->free_head].addr = addr; ... if (end) remove the VRING_DESC_F_NEXT flag }
What do you think? We can also combine the two functions into one.
Best, Wei
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