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skb: report completion status for zero copy skbs 

Even if skb is marked for zero copy, net core might still decide
to copy it later which is somewhat slower than a copy in user context:
besides copying the data we need to pin/unpin the pages.

Add a parameter reporting such cases through zero copy callback:
if this happens a lot, device can take this into account
and switch to copying in user context.

This patch updates all users but ignores the passed value for now:
it will be used by follow-up patches.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Michael S. Tsirkin 2012-11-01 09:16:22 +00:00 committed by David S. Miller
parent 202975b4c5
commit e19d6763cc
4 changed files with 7 additions and 5 deletions
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2
drivers/vhost/vhost.c
View File

@ -1600,7 +1600,7 @@ void vhost_ubuf_put_and_wait(struct vhost_ubuf_ref *ubufs)
kfree(ubufs);
}
void vhost_zerocopy_callback(struct ubuf_info *ubuf)
void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool status)
{
struct vhost_ubuf_ref *ubufs = ubuf->ctx;
struct vhost_virtqueue *vq = ubufs->vq;

2
drivers/vhost/vhost.h
View File

@ -191,7 +191,7 @@ bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
unsigned int log_num, u64 len);
void vhost_zerocopy_callback(struct ubuf_info *);
void vhost_zerocopy_callback(struct ubuf_info *, bool);
int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq);
#define vq_err(vq, fmt, ...) do { \

4
include/linux/skbuff.h
View File

@ -235,11 +235,13 @@ enum {
/*
* The callback notifies userspace to release buffers when skb DMA is done in
* lower device, the skb last reference should be 0 when calling this.
* The zerocopy_success argument is true if zero copy transmit occurred,
* false on data copy or out of memory error caused by data copy attempt.
* The ctx field is used to track device context.
* The desc field is used to track userspace buffer index.
*/
struct ubuf_info {
void (*callback)(struct ubuf_info *);
void (*callback)(struct ubuf_info *, bool zerocopy_success);
void *ctx;
unsigned long desc;
};

4
net/core/skbuff.c
View File

@ -519,7 +519,7 @@ static void skb_release_data(struct sk_buff *skb)
uarg = skb_shinfo(skb)->destructor_arg;
if (uarg->callback)
uarg->callback(uarg);
uarg->callback(uarg, true);
}
if (skb_has_frag_list(skb))
@ -797,7 +797,7 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
for (i = 0; i < num_frags; i++)
skb_frag_unref(skb, i);
uarg->callback(uarg);
uarg->callback(uarg, false);
/* skb frags point to kernel buffers */
for (i = num_frags - 1; i >= 0; i--) {