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Commit 43e9d194 authored by Wei Liu's avatar Wei Liu Committed by David S. Miller
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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: default avatarWei Liu <wei.liu2@citrix.com>
Acked-by: default avatarIan Campbell <ian.campbell@citrix.com>
Acked-by: default avatarMatt Wilson <msw@amazon.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5b2941b1

drivers/net/xen-netback/netback.c

+2 −75
Original line number Diff line number Diff line
@@ -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;



			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.u.gmfn = virt_to_mfn(page_address(page));



		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);

	}