Wei Liu
2013-Aug-26 11:59 UTC
[PATCH net-next 1/3] xen-netback: remove page tracking facility
The data flow from DomU to DomU on the same host in current copying
scheme with tracking facility:
copy
DomU --------> Dom0 DomU
| ^
|____________________________|
copy
The page in Dom0 is a page with valid MFN. So we can always copy from
page Dom0, thus removing the need for a tracking facility.
copy copy
DomU --------> Dom0 -------> DomU
Simple iperf test shows no performance regression (obviously we copy
twice either way):
W/ tracking: ~5.3Gb/s
W/o tracking: ~5.4Gb/s
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Matt Wilson <msw@amazon.com>
---
drivers/net/xen-netback/netback.c | 77 +------------------------------------
1 file changed, 2 insertions(+), 75 deletions(-)
diff --git a/drivers/net/xen-netback/netback.c
b/drivers/net/xen-netback/netback.c
index 64828de..91f163d 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -95,21 +95,6 @@ struct netbk_rx_meta {
#define MAX_BUFFER_OFFSET PAGE_SIZE
-/* extra field used in struct page */
-union page_ext {
- struct {
-#if BITS_PER_LONG < 64
-#define IDX_WIDTH 8
-#define GROUP_WIDTH (BITS_PER_LONG - IDX_WIDTH)
- unsigned int group:GROUP_WIDTH;
- unsigned int idx:IDX_WIDTH;
-#else
- unsigned int group, idx;
-#endif
- } e;
- void *mapping;
-};
-
struct xen_netbk {
wait_queue_head_t wq;
struct task_struct *task;
@@ -214,45 +199,6 @@ static inline unsigned long idx_to_kaddr(struct xen_netbk
*netbk,
return (unsigned long)pfn_to_kaddr(idx_to_pfn(netbk, idx));
}
-/* extra field used in struct page */
-static inline void set_page_ext(struct page *pg, struct xen_netbk *netbk,
- unsigned int idx)
-{
- unsigned int group = netbk - xen_netbk;
- union page_ext ext = { .e = { .group = group + 1, .idx = idx } };
-
- BUILD_BUG_ON(sizeof(ext) > sizeof(ext.mapping));
- pg->mapping = ext.mapping;
-}
-
-static int get_page_ext(struct page *pg,
- unsigned int *pgroup, unsigned int *pidx)
-{
- union page_ext ext = { .mapping = pg->mapping };
- struct xen_netbk *netbk;
- unsigned int group, idx;
-
- group = ext.e.group - 1;
-
- if (group < 0 || group >= xen_netbk_group_nr)
- return 0;
-
- netbk = &xen_netbk[group];
-
- idx = ext.e.idx;
-
- if ((idx < 0) || (idx >= MAX_PENDING_REQS))
- return 0;
-
- if (netbk->mmap_pages[idx] != pg)
- return 0;
-
- *pgroup = group;
- *pidx = idx;
-
- return 1;
-}
-
/*
* This is the amount of packet we copy rather than map, so that the
* guest can''t fiddle with the contents of the headers while we do
@@ -453,12 +399,6 @@ static void netbk_gop_frag_copy(struct xenvif *vif, struct
sk_buff *skb,
{
struct gnttab_copy *copy_gop;
struct netbk_rx_meta *meta;
- /*
- * These variables are used iff get_page_ext returns true,
- * in which case they are guaranteed to be initialized.
- */
- unsigned int uninitialized_var(group), uninitialized_var(idx);
- int foreign = get_page_ext(page, &group, &idx);
unsigned long bytes;
/* Data must not cross a page boundary. */
@@ -494,20 +434,9 @@ static void netbk_gop_frag_copy(struct xenvif *vif, struct
sk_buff *skb,
copy_gop = npo->copy + npo->copy_prod++;
copy_gop->flags = GNTCOPY_dest_gref;
- if (foreign) {
- struct xen_netbk *netbk = &xen_netbk[group];
- struct pending_tx_info *src_pend;
+ copy_gop->source.domid = DOMID_SELF;
+ copy_gop->source.u.gmfn = virt_to_mfn(page_address(page));
- src_pend = &netbk->pending_tx_info[idx];
-
- copy_gop->source.domid = src_pend->vif->domid;
- copy_gop->source.u.ref = src_pend->req.gref;
- copy_gop->flags |= GNTCOPY_source_gref;
- } else {
- void *vaddr = page_address(page);
- copy_gop->source.domid = DOMID_SELF;
- copy_gop->source.u.gmfn = virt_to_mfn(vaddr);
- }
copy_gop->source.offset = offset;
copy_gop->dest.domid = vif->domid;
@@ -1047,7 +976,6 @@ static struct page *xen_netbk_alloc_page(struct xen_netbk
*netbk,
page = alloc_page(GFP_KERNEL|__GFP_COLD);
if (!page)
return NULL;
- set_page_ext(page, netbk, pending_idx);
netbk->mmap_pages[pending_idx] = page;
return page;
}
@@ -1155,7 +1083,6 @@ static struct gnttab_copy *xen_netbk_get_requests(struct
xen_netbk *netbk,
first->req.offset = 0;
first->req.size = dst_offset;
first->head = start_idx;
- set_page_ext(page, netbk, head_idx);
netbk->mmap_pages[head_idx] = page;
frag_set_pending_idx(&frags[shinfo->nr_frags], head_idx);
}
--
1.7.10.4