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xen-netback: remove page tracking facility

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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>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Wei Liu 2013-08-26 12:59:37 +01:00 committed by David S. Miller
parent 5b2941b18d
commit 43e9d19432
1 changed files with 2 additions and 75 deletions
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77
drivers/net/xen-netback/netback.c
View file

@ -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);
}