Below should be useful for some experiments Jason is doing.
I thought I'd send it out for early review/feedback.
Compiled-only at this point.
event idx feature allows us to defer interrupts until
a specific # of descriptors were used.
Sometimes it might be useful to get an interrupt after
a specific descriptor, regardless.
This adds a descriptor flag for this, and an API
to create an urgent output descriptor.
This is still an RFC:
we'll need a feature bit for drivers to detect this,
but we've run out of feature bits for virtio 0.X.
For experimentation purposes, drivers can assume
this is set, or add a driver-specific feature bit.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
include/linux/virtio.h | 6 ++++++
include/uapi/linux/virtio_ring.h | 3 +++
drivers/virtio/virtio_ring.c | 46 ++++++++++++++++++++++++++++++++++++----
3 files changed, 51 insertions(+), 4 deletions(-)
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b46671e..14625a6 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -39,6 +39,12 @@ int virtqueue_add_outbuf(struct virtqueue *vq,
void *data,
gfp_t gfp);
+int virtqueue_add_outbuf_urgent(struct virtqueue *vq,
+ struct scatterlist sg[], unsigned int num,
+ void *data,
+ gfp_t gfp);
+
+
int virtqueue_add_inbuf(struct virtqueue *vq,
struct scatterlist sg[], unsigned int num,
void *data,
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index a99f9b7..d08b1e6 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -39,6 +39,9 @@
#define VRING_DESC_F_WRITE 2
/* This means the buffer contains a list of buffer descriptors. */
#define VRING_DESC_F_INDIRECT 4
+/* This means the descriptor should cause an interrupt
+ * ignoring avail event idx. */
+#define VRING_DESC_F_URGENT 8
/* The Host uses this in used->flags to advise the Guest: don't kick me when
* you add a buffer. It's unreliable, so it's simply an optimization. Guest
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 4d08f45a..3e448b9 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -115,6 +115,7 @@ static inline struct scatterlist *sg_next_arr(struct scatterlist *sg,
/* Set up an indirect table of descriptors and add it to the queue. */
static inline int vring_add_indirect(struct vring_virtqueue *vq,
+ bool urgent,
struct scatterlist *sgs[],
struct scatterlist *(*next)
(struct scatterlist *, unsigned int *),
@@ -173,6 +174,8 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
/* Use a single buffer which doesn't continue */
head = vq->free_head;
vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
+ if (urgent)
+ vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
vq->vring.desc[head].addr = virt_to_phys(desc);
/* kmemleak gives a false positive, as it's hidden by virt_to_phys */
kmemleak_ignore(desc);
@@ -185,6 +188,7 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
}
static inline int virtqueue_add(struct virtqueue *_vq,
+ bool urgent,
struct scatterlist *sgs[],
struct scatterlist *(*next)
(struct scatterlist *, unsigned int *),
@@ -227,7 +231,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
/* If the host supports indirect descriptor tables, and we have multiple
* buffers, then go indirect. FIXME: tune this threshold */
if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
- head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
+ head = vring_add_indirect(vq, urgent, sgs, next, total_sg, total_out,
total_in,
out_sgs, in_sgs, gfp);
if (likely(head >= 0))
@@ -256,6 +260,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
for (n = 0; n < out_sgs; n++) {
for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
+ if (urgent) {
+ vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
+ urgent = false;
+ }
vq->vring.desc[i].addr = sg_phys(sg);
vq->vring.desc[i].len = sg->length;
prev = i;
@@ -265,6 +273,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
for (; n < (out_sgs + in_sgs); n++) {
for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
+ if (urgent) {
+ vq->vring.desc[head].flags |= VRING_DESC_F_URGENT;
+ urgent = false;
+ }
vq->vring.desc[i].addr = sg_phys(sg);
vq->vring.desc[i].len = sg->length;
prev = i;
@@ -305,6 +317,8 @@ add_head:
/**
* virtqueue_add_sgs - expose buffers to other end
+ * @urgent: in case virtqueue_enable_cb_delayed was called, cause an interrupt
+ * after this descriptor was completed
* @vq: the struct virtqueue we're talking about.
* @sgs: array of terminated scatterlists.
* @out_num: the number of scatterlists readable by other side
@@ -337,7 +351,7 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
for (sg = sgs[i]; sg; sg = sg_next(sg))
total_in++;
}
- return virtqueue_add(_vq, sgs, sg_next_chained,
+ return virtqueue_add(_vq, false, sgs, sg_next_chained,
total_out, total_in, out_sgs, in_sgs, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
@@ -360,11 +374,35 @@ int virtqueue_add_outbuf(struct virtqueue *vq,
void *data,
gfp_t gfp)
{
- return virtqueue_add(vq, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
+ return virtqueue_add(vq, false, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
/**
+ * virtqueue_add_outbuf - expose output buffers to other end
+ * in case virtqueue_enable_cb_delayed was called, cause an interrupt
+ * after this descriptor was completed
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists readable by other side
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
+ */
+int virtqueue_add_outbuf_urgent(struct virtqueue *vq,
+ struct scatterlist sg[], unsigned int num,
+ void *data,
+ gfp_t gfp)
+{
+ return virtqueue_add(vq, true, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_outbuf_urgent);
+
+/**
* virtqueue_add_inbuf - expose input buffers to other end
* @vq: the struct virtqueue we're talking about.
* @sgs: array of scatterlists (need not be terminated!)
@@ -382,7 +420,7 @@ int virtqueue_add_inbuf(struct virtqueue *vq,
void *data,
gfp_t gfp)
{
- return virtqueue_add(vq, &sg, sg_next_arr, 0, num, 0, 1, data, gfp);
+ return virtqueue_add(vq, false, &sg, sg_next_arr, 0, num, 0, 1, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
--
MST
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