In big mode, pre-mapping DMA is beneficial because if the pages are not
used, we can reuse them without needing to unmap and remap.
We require space to store the DMA address. I use the page.dma_addr to
store the DMA address from the pp structure inside the page.
Every page retrieved from get_a_page() is mapped, and its DMA address is
stored in page.dma_addr. When a page is returned to the chain, we check
the DMA status; if it is not mapped (potentially having been unmapped),
we remap it before returning it to the chain.
Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com>
---
drivers/net/virtio_net.c | 98 +++++++++++++++++++++++++++++++++-------
1 file changed, 81 insertions(+), 17 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4446fb54de6d..7ea7e9bcd5d7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -50,6 +50,7 @@ module_param(napi_tx, bool, 0644);
#define page_chain_next(p) ((struct page *)((p)->pp))
#define page_chain_add(p, n) ((p)->pp = (void *)n)
+#define page_dma_addr(p) ((p)->dma_addr)
/* RX packet size EWMA. The average packet size is used to determine the packet
* buffer size when refilling RX rings. As the entire RX ring may be refilled
@@ -434,6 +435,46 @@ skb_vnet_common_hdr(struct sk_buff *skb)
return (struct virtio_net_common_hdr *)skb->cb;
}
+static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
+{
+ sg->dma_address = addr;
+ sg->length = len;
+}
+
+static void page_chain_unmap(struct receive_queue *rq, struct page *p)
+{
+ virtqueue_dma_unmap_page_attrs(rq->vq, page_dma_addr(p), PAGE_SIZE,
+ DMA_FROM_DEVICE, 0);
+
+ page_dma_addr(p) = DMA_MAPPING_ERROR;
+}
+
+static int page_chain_map(struct receive_queue *rq, struct page *p)
+{
+ dma_addr_t addr;
+
+ addr = virtqueue_dma_map_page_attrs(rq->vq, p, 0, PAGE_SIZE,
DMA_FROM_DEVICE, 0);
+ if (virtqueue_dma_mapping_error(rq->vq, addr))
+ return -ENOMEM;
+
+ page_dma_addr(p) = addr;
+ return 0;
+}
+
+static void page_chain_release(struct receive_queue *rq)
+{
+ struct page *p, *n;
+
+ for (p = rq->pages; p; p = n) {
+ n = page_chain_next(p);
+
+ page_chain_unmap(rq, p);
+ __free_pages(p, 0);
+ }
+
+ rq->pages = NULL;
+}
+
/*
* put the whole most recent used list in the beginning for reuse
*/
@@ -441,6 +482,13 @@ static void give_pages(struct receive_queue *rq, struct
page *page)
{
struct page *end;
+ if (page_dma_addr(page) == DMA_MAPPING_ERROR) {
+ if (page_chain_map(rq, page)) {
+ __free_pages(page, 0);
+ return;
+ }
+ }
+
/* Find end of list, sew whole thing into vi->rq.pages. */
for (end = page; page_chain_next(end); end = page_chain_next(end));
@@ -456,8 +504,15 @@ static struct page *get_a_page(struct receive_queue *rq,
gfp_t gfp_mask)
rq->pages = page_chain_next(p);
/* clear chain here, it is used to chain pages */
page_chain_add(p, NULL);
- } else
+ } else {
p = alloc_page(gfp_mask);
+
+ if (page_chain_map(rq, p)) {
+ __free_pages(p, 0);
+ return NULL;
+ }
+ }
+
return p;
}
@@ -613,8 +668,6 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
return NULL;
page = page_chain_next(page);
- if (page)
- give_pages(rq, page);
goto ok;
}
@@ -640,6 +693,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
skb_add_rx_frag(skb, 0, page, offset, len, truesize);
else
page_to_free = page;
+ page = NULL;
goto ok;
}
@@ -657,6 +711,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
BUG_ON(offset >= PAGE_SIZE);
while (len) {
unsigned int frag_size = min((unsigned)PAGE_SIZE - offset, len);
+
+ /* unmap the page before using it. */
+ if (!offset)
+ page_chain_unmap(rq, page);
+
skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset,
frag_size, truesize);
len -= frag_size;
@@ -664,15 +723,15 @@ static struct sk_buff *page_to_skb(struct virtnet_info
*vi,
offset = 0;
}
- if (page)
- give_pages(rq, page);
-
ok:
hdr = skb_vnet_common_hdr(skb);
memcpy(hdr, hdr_p, hdr_len);
if (page_to_free)
put_page(page_to_free);
+ if (page)
+ give_pages(rq, page);
+
return skb;
}
@@ -823,7 +882,8 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq,
void *buf)
rq = &vi->rq[i];
- if (rq->do_dma)
+ /* Skip the unmap for big mode. */
+ if (!vi->big_packets || vi->mergeable_rx_bufs)
virtnet_rq_unmap(rq, buf, 0);
virtnet_rq_free_buf(vi, rq, buf);
@@ -1346,8 +1406,12 @@ static struct sk_buff *receive_big(struct net_device
*dev,
struct virtnet_rq_stats *stats)
{
struct page *page = buf;
- struct sk_buff *skb =
- page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, 0);
+ struct sk_buff *skb;
+
+ /* Unmap first page. The follow code may read this page. */
+ page_chain_unmap(rq, page);
+
+ skb = page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, 0);
u64_stats_add(&stats->bytes, len - vi->hdr_len);
if (unlikely(!skb))
@@ -1896,7 +1960,7 @@ static int add_recvbuf_big(struct virtnet_info *vi,
struct receive_queue *rq,
gfp_t gfp)
{
struct page *first, *list = NULL;
- char *p;
+ dma_addr_t p;
int i, err, offset;
sg_init_table(rq->sg, vi->big_packets_num_skbfrags + 2);
@@ -1909,7 +1973,7 @@ static int add_recvbuf_big(struct virtnet_info *vi,
struct receive_queue *rq,
give_pages(rq, list);
return -ENOMEM;
}
- sg_set_buf(&rq->sg[i], page_address(first), PAGE_SIZE);
+ sg_fill_dma(&rq->sg[i], page_dma_addr(first), PAGE_SIZE);
/* chain new page in list head to match sg */
page_chain_add(first, list);
@@ -1921,15 +1985,16 @@ static int add_recvbuf_big(struct virtnet_info *vi,
struct receive_queue *rq,
give_pages(rq, list);
return -ENOMEM;
}
- p = page_address(first);
+
+ p = page_dma_addr(first);
/* rq->sg[0], rq->sg[1] share the same page */
/* a separated rq->sg[0] for header - required in case !any_header_sg */
- sg_set_buf(&rq->sg[0], p, vi->hdr_len);
+ sg_fill_dma(&rq->sg[0], p, vi->hdr_len);
/* rq->sg[1] for data packet, from offset */
offset = sizeof(struct padded_vnet_hdr);
- sg_set_buf(&rq->sg[1], p + offset, PAGE_SIZE - offset);
+ sg_fill_dma(&rq->sg[1], p + offset, PAGE_SIZE - offset);
/* chain first in list head */
page_chain_add(first, list);
@@ -2131,7 +2196,7 @@ static int virtnet_receive(struct receive_queue *rq, int
budget,
}
} else {
while (packets < budget &&
- (buf = virtnet_rq_get_buf(rq, &len, NULL)) != NULL) {
+ (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
packets++;
}
@@ -4252,8 +4317,7 @@ static void _free_receive_bufs(struct virtnet_info *vi)
int i;
for (i = 0; i < vi->max_queue_pairs; i++) {
- while (vi->rq[i].pages)
- __free_pages(get_a_page(&vi->rq[i], GFP_KERNEL), 0);
+ page_chain_release(&vi->rq[i]);
old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
RCU_INIT_POINTER(vi->rq[i].xdp_prog, NULL);
--
2.32.0.3.g01195cf9f
