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Revert "xen-netback: improve ring effeciency for guest RX"
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This reverts commit 4f0581d.

The named changeset is causing problem. Let's aim to make this part less
fragile before trying to improve things.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Annie Li <annie.li@oracle.com>
Cc: Matt Wilson <msw@amazon.com>
Cc: Xi Xiong <xixiong@amazon.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Wei Liu authored and David S. Miller committed Oct 8, 2013
1 parent 0ca4520 commit 33bc801
Showing 1 changed file with 83 additions and 61 deletions.
144 changes: 83 additions & 61 deletions drivers/net/xen-netback/netback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,14 +47,6 @@
#include <asm/xen/hypercall.h>
#include <asm/xen/page.h>

/* SKB control block overlay is used to store useful information when
* doing guest RX.
*/
struct skb_cb_overlay {
int meta_slots_used;
int peek_slots_count;
};

/* Provide an option to disable split event channels at load time as
* event channels are limited resource. Split event channels are
* enabled by default.
Expand Down Expand Up @@ -220,60 +212,90 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
return false;
}

struct xenvif_count_slot_state {
unsigned long copy_off;
bool head;
};

unsigned int xenvif_count_frag_slots(struct xenvif *vif,
unsigned long offset, unsigned long size,
struct xenvif_count_slot_state *state)
{
unsigned count = 0;

offset &= ~PAGE_MASK;

while (size > 0) {
unsigned long bytes;

bytes = PAGE_SIZE - offset;

if (bytes > size)
bytes = size;

if (start_new_rx_buffer(state->copy_off, bytes, state->head)) {
count++;
state->copy_off = 0;
}

if (state->copy_off + bytes > MAX_BUFFER_OFFSET)
bytes = MAX_BUFFER_OFFSET - state->copy_off;

state->copy_off += bytes;

offset += bytes;
size -= bytes;

if (offset == PAGE_SIZE)
offset = 0;

state->head = false;
}

return count;
}

/*
* Figure out how many ring slots we're going to need to send @skb to
* the guest. This function is essentially a dry run of
* xenvif_gop_frag_copy.
*/
unsigned int xenvif_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
{
struct xenvif_count_slot_state state;
unsigned int count;
int i, copy_off;
struct skb_cb_overlay *sco;
unsigned char *data;
unsigned i;

count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE);
state.head = true;
state.copy_off = 0;

copy_off = skb_headlen(skb) % PAGE_SIZE;
/* Slot for the first (partial) page of data. */
count = 1;

/* Need a slot for the GSO prefix for GSO extra data? */
if (skb_shinfo(skb)->gso_size)
count++;

for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;
unsigned long bytes;

offset &= ~PAGE_MASK;

while (size > 0) {
BUG_ON(offset >= PAGE_SIZE);
BUG_ON(copy_off > MAX_BUFFER_OFFSET);

bytes = PAGE_SIZE - offset;

if (bytes > size)
bytes = size;
data = skb->data;
while (data < skb_tail_pointer(skb)) {
unsigned long offset = offset_in_page(data);
unsigned long size = PAGE_SIZE - offset;

if (start_new_rx_buffer(copy_off, bytes, 0)) {
count++;
copy_off = 0;
}
if (data + size > skb_tail_pointer(skb))
size = skb_tail_pointer(skb) - data;

if (copy_off + bytes > MAX_BUFFER_OFFSET)
bytes = MAX_BUFFER_OFFSET - copy_off;
count += xenvif_count_frag_slots(vif, offset, size, &state);

copy_off += bytes;
data += size;
}

offset += bytes;
size -= bytes;
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;

if (offset == PAGE_SIZE)
offset = 0;
}
count += xenvif_count_frag_slots(vif, offset, size, &state);
}

sco = (struct skb_cb_overlay *)skb->cb;
sco->peek_slots_count = count;
return count;
}

Expand Down Expand Up @@ -305,11 +327,14 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
return meta;
}

/* Set up the grant operations for this fragment. */
/*
* Set up the grant operations for this fragment. If it's a flipping
* interface, we also set up the unmap request from here.
*/
static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
struct netrx_pending_operations *npo,
struct page *page, unsigned long size,
unsigned long offset, int head, int *first)
unsigned long offset, int *head)
{
struct gnttab_copy *copy_gop;
struct xenvif_rx_meta *meta;
Expand All @@ -333,12 +358,12 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
if (bytes > size)
bytes = size;

if (start_new_rx_buffer(npo->copy_off, bytes, head)) {
if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
/*
* Netfront requires there to be some data in the head
* buffer.
*/
BUG_ON(*first);
BUG_ON(*head);

meta = get_next_rx_buffer(vif, npo);
}
Expand Down Expand Up @@ -372,10 +397,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
}

/* Leave a gap for the GSO descriptor. */
if (*first && skb_shinfo(skb)->gso_size && !vif->gso_prefix)
if (*head && skb_shinfo(skb)->gso_size && !vif->gso_prefix)
vif->rx.req_cons++;

*first = 0; /* There must be something in this buffer now. */
*head = 0; /* There must be something in this buffer now. */

}
}
Expand All @@ -401,7 +426,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
struct xen_netif_rx_request *req;
struct xenvif_rx_meta *meta;
unsigned char *data;
int first = 1;
int head = 1;
int old_meta_prod;

old_meta_prod = npo->meta_prod;
Expand Down Expand Up @@ -437,7 +462,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
len = skb_tail_pointer(skb) - data;

xenvif_gop_frag_copy(vif, skb, npo,
virt_to_page(data), len, offset, 1, &first);
virt_to_page(data), len, offset, &head);
data += len;
}

Expand All @@ -446,7 +471,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
skb_frag_page(&skb_shinfo(skb)->frags[i]),
skb_frag_size(&skb_shinfo(skb)->frags[i]),
skb_shinfo(skb)->frags[i].page_offset,
0, &first);
&head);
}

return npo->meta_prod - old_meta_prod;
Expand Down Expand Up @@ -504,6 +529,10 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
}
}

struct skb_cb_overlay {
int meta_slots_used;
};

static void xenvif_kick_thread(struct xenvif *vif)
{
wake_up(&vif->wq);
Expand Down Expand Up @@ -534,26 +563,19 @@ void xenvif_rx_action(struct xenvif *vif)
count = 0;

while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
RING_IDX old_rx_req_cons;

vif = netdev_priv(skb->dev);
nr_frags = skb_shinfo(skb)->nr_frags;

old_rx_req_cons = vif->rx.req_cons;
sco = (struct skb_cb_overlay *)skb->cb;
sco->meta_slots_used = xenvif_gop_skb(skb, &npo);

count += vif->rx.req_cons - old_rx_req_cons;
count += nr_frags + 1;

__skb_queue_tail(&rxq, skb);

skb = skb_peek(&vif->rx_queue);
if (skb == NULL)
break;
sco = (struct skb_cb_overlay *)skb->cb;

/* Filled the batch queue? */
if (count + sco->peek_slots_count >= XEN_NETIF_RX_RING_SIZE)
/* XXX FIXME: RX path dependent on MAX_SKB_FRAGS */
if (count + MAX_SKB_FRAGS >= XEN_NETIF_RX_RING_SIZE)
break;
}

Expand Down

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