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Message-Id: <20210824102809.26370-4-jgross@suse.com>
Date: Tue, 24 Aug 2021 12:28:08 +0200
From: Juergen Gross <jgross@...e.com>
To: xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Juergen Gross <jgross@...e.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Stefano Stabellini <sstabellini@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH v2 3/4] xen/netfront: disentangle tx_skb_freelist
The tx_skb_freelist elements are in a single linked list with the
request id used as link reference. The per element link field is in a
union with the skb pointer of an in use request.
Move the link reference out of the union in order to enable a later
reuse of it for requests which need a populated skb pointer.
Rename add_id_to_freelist() and get_id_from_freelist() to
add_id_to_list() and get_id_from_list() in order to prepare using
those for other lists as well. Define ~0 as value to indicate the end
of a list and place that value into the link for a request not being
on the list.
When freeing a skb zero the skb pointer in the request. Use a NULL
value of the skb pointer instead of skb_entry_is_link() for deciding
whether a request has a skb linked to it.
Remove skb_entry_set_link() and open code it instead as it is really
trivial now.
Signed-off-by: Juergen Gross <jgross@...e.com>
---
V2:
- new patch
---
drivers/net/xen-netfront.c | 61 ++++++++++++++++----------------------
1 file changed, 25 insertions(+), 36 deletions(-)
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 714fe9d2c534..956e1266bd1a 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -126,17 +126,11 @@ struct netfront_queue {
/*
* {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries
- * are linked from tx_skb_freelist through skb_entry.link.
- *
- * NB. Freelist index entries are always going to be less than
- * PAGE_OFFSET, whereas pointers to skbs will always be equal or
- * greater than PAGE_OFFSET: we use this property to distinguish
- * them.
+ * are linked from tx_skb_freelist through tx_link.
*/
- union skb_entry {
- struct sk_buff *skb;
- unsigned long link;
- } tx_skbs[NET_TX_RING_SIZE];
+ struct sk_buff *tx_skbs[NET_TX_RING_SIZE];
+ unsigned short tx_link[NET_TX_RING_SIZE];
+#define TX_LINK_NONE 0xffff
grant_ref_t gref_tx_head;
grant_ref_t grant_tx_ref[NET_TX_RING_SIZE];
struct page *grant_tx_page[NET_TX_RING_SIZE];
@@ -181,33 +175,25 @@ struct netfront_rx_info {
struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
};
-static void skb_entry_set_link(union skb_entry *list, unsigned short id)
-{
- list->link = id;
-}
-
-static int skb_entry_is_link(const union skb_entry *list)
-{
- BUILD_BUG_ON(sizeof(list->skb) != sizeof(list->link));
- return (unsigned long)list->skb < PAGE_OFFSET;
-}
-
/*
* Access macros for acquiring freeing slots in tx_skbs[].
*/
-static void add_id_to_freelist(unsigned *head, union skb_entry *list,
- unsigned short id)
+static void add_id_to_list(unsigned *head, unsigned short *list,
+ unsigned short id)
{
- skb_entry_set_link(&list[id], *head);
+ list[id] = *head;
*head = id;
}
-static unsigned short get_id_from_freelist(unsigned *head,
- union skb_entry *list)
+static unsigned short get_id_from_list(unsigned *head, unsigned short *list)
{
unsigned int id = *head;
- *head = list[id].link;
+
+ if (id != TX_LINK_NONE) {
+ *head = list[id];
+ list[id] = TX_LINK_NONE;
+ }
return id;
}
@@ -406,7 +392,8 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
continue;
id = txrsp.id;
- skb = queue->tx_skbs[id].skb;
+ skb = queue->tx_skbs[id];
+ queue->tx_skbs[id] = NULL;
if (unlikely(gnttab_query_foreign_access(
queue->grant_tx_ref[id]) != 0)) {
pr_alert("%s: warning -- grant still in use by backend domain\n",
@@ -419,7 +406,7 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
&queue->gref_tx_head, queue->grant_tx_ref[id]);
queue->grant_tx_ref[id] = GRANT_INVALID_REF;
queue->grant_tx_page[id] = NULL;
- add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, id);
+ add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, id);
dev_kfree_skb_irq(skb);
}
@@ -452,7 +439,7 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
struct netfront_queue *queue = info->queue;
struct sk_buff *skb = info->skb;
- id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs);
+ id = get_id_from_list(&queue->tx_skb_freelist, queue->tx_link);
tx = RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++);
ref = gnttab_claim_grant_reference(&queue->gref_tx_head);
WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));
@@ -460,7 +447,7 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id,
gfn, GNTMAP_readonly);
- queue->tx_skbs[id].skb = skb;
+ queue->tx_skbs[id] = skb;
queue->grant_tx_page[id] = page;
queue->grant_tx_ref[id] = ref;
@@ -1284,17 +1271,18 @@ static void xennet_release_tx_bufs(struct netfront_queue *queue)
for (i = 0; i < NET_TX_RING_SIZE; i++) {
/* Skip over entries which are actually freelist references */
- if (skb_entry_is_link(&queue->tx_skbs[i]))
+ if (!queue->tx_skbs[i])
continue;
- skb = queue->tx_skbs[i].skb;
+ skb = queue->tx_skbs[i];
+ queue->tx_skbs[i] = NULL;
get_page(queue->grant_tx_page[i]);
gnttab_end_foreign_access(queue->grant_tx_ref[i],
GNTMAP_readonly,
(unsigned long)page_address(queue->grant_tx_page[i]));
queue->grant_tx_page[i] = NULL;
queue->grant_tx_ref[i] = GRANT_INVALID_REF;
- add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, i);
+ add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, i);
dev_kfree_skb_irq(skb);
}
}
@@ -1851,13 +1839,14 @@ static int xennet_init_queue(struct netfront_queue *queue)
snprintf(queue->name, sizeof(queue->name), "vif%s-q%u",
devid, queue->id);
- /* Initialise tx_skbs as a free chain containing every entry. */
+ /* Initialise tx_skb_freelist as a free chain containing every entry. */
queue->tx_skb_freelist = 0;
for (i = 0; i < NET_TX_RING_SIZE; i++) {
- skb_entry_set_link(&queue->tx_skbs[i], i+1);
+ queue->tx_link[i] = i + 1;
queue->grant_tx_ref[i] = GRANT_INVALID_REF;
queue->grant_tx_page[i] = NULL;
}
+ queue->tx_link[NET_TX_RING_SIZE - 1] = TX_LINK_NONE;
/* Clear out rx_skbs */
for (i = 0; i < NET_RX_RING_SIZE; i++) {
--
2.26.2
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