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SubjectRE: [Xen-devel] [PATCH net-next RFC 2/5] xen-netback: Change TX path from grant copy to mapping
Date
> -----Original Message-----
> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel-
> bounces@lists.xen.org] On Behalf Of Zoltan Kiss
> Sent: 30 October 2013 00:50
> To: Ian Campbell; Wei Liu; xen-devel@lists.xenproject.org;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Jonathan Davies
> Cc: Zoltan Kiss
> Subject: [Xen-devel] [PATCH net-next RFC 2/5] xen-netback: Change TX path
> from grant copy to mapping
>
> This patch changes the grant copy on the TX patch to grant mapping
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> ---
> drivers/net/xen-netback/interface.c | 39 +++++-
> drivers/net/xen-netback/netback.c | 241 +++++++++++++--------------------
> --
> 2 files changed, 126 insertions(+), 154 deletions(-)
>
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-
> netback/interface.c
> index f5c3c57..fb16ede 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -336,8 +336,20 @@ struct xenvif *xenvif_alloc(struct device *parent,
> domid_t domid,
> vif->pending_prod = MAX_PENDING_REQS;
> for (i = 0; i < MAX_PENDING_REQS; i++)
> vif->pending_ring[i] = i;
> - for (i = 0; i < MAX_PENDING_REQS; i++)
> - vif->mmap_pages[i] = NULL;
> + err = alloc_xenballooned_pages(MAX_PENDING_REQS,
> + vif->mmap_pages,
> + false);

Since this is a per-vif allocation, is this going to scale?

> + if (err) {
> + netdev_err(dev, "Could not reserve mmap_pages\n");
> + return NULL;
> + }
> + for (i = 0; i < MAX_PENDING_REQS; i++) {
> + vif->pending_tx_info[i].callback_struct = (struct ubuf_info)
> + { .callback = xenvif_zerocopy_callback,
> + .ctx = NULL,
> + .desc = i };
> + vif->grant_tx_handle[i] = NETBACK_INVALID_HANDLE;
> + }
>
> /*
> * Initialise a dummy MAC address. We choose the numerically
> @@ -481,11 +493,34 @@ void xenvif_disconnect(struct xenvif *vif)
>
> void xenvif_free(struct xenvif *vif)
> {
> + int i;
> +
> netif_napi_del(&vif->napi);
>
> unregister_netdev(vif->dev);
>
> free_netdev(vif->dev);
>
> + /* FIXME: This is a workaround for 2 problems:
> + * - the guest sent a packet just before teardown, and it is still not
> + * delivered
> + * - the stack forgot to notify us that we can give back a slot
> + * For the first problem we shouldn't do this, as the skb might still
> + * access that page. I will come up with a more robust solution later.
> + * The second is definitely a bug, it leaks a slot from the ring
> + * forever.
> + * Classic kernel patchset has delayed copy for that, we might want to
> + * reuse that?

I think you're going to have to. You can't have once guest left at the mercy of another; if the mapping sticks around for too long then you really need the copy-aside.

> + */
> + for (i = 0; i < MAX_PENDING_REQS; ++i) {
> + if (vif->grant_tx_handle[i] != NETBACK_INVALID_HANDLE) {
> + netdev_err(vif->dev,
> + "Page still granted! Index: %x\n", i);
> + xenvif_idx_unmap(vif, i);
> + }
> + }
> +
> + free_xenballooned_pages(MAX_PENDING_REQS, vif-
> >mmap_pages);
> +
> module_put(THIS_MODULE);
> }
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> index 10470dc..e544e9f 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -883,10 +883,10 @@ static inline void xenvif_tx_create_gop(struct
> xenvif *vif, u16 pending_idx,
>
> }
>
> -static struct gnttab_copy *xenvif_get_requests(struct xenvif *vif,
> +static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif
> *vif,
> struct sk_buff *skb,
> struct xen_netif_tx_request *txp,
> - struct gnttab_copy *gop)
> + struct gnttab_map_grant_ref
> *gop)
> {
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> skb_frag_t *frags = shinfo->frags;
> @@ -907,83 +907,12 @@ static struct gnttab_copy
> *xenvif_get_requests(struct xenvif *vif,
> /* Skip first skb fragment if it is on same page as header fragment. */
> start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
>
> - /* Coalesce tx requests, at this point the packet passed in
> - * should be <= 64K. Any packets larger than 64K have been
> - * handled in xenvif_count_requests().
> - */
> - for (shinfo->nr_frags = slot = start; slot < nr_slots;
> - shinfo->nr_frags++) {
> - struct pending_tx_info *pending_tx_info =
> - vif->pending_tx_info;
> -
> - page = alloc_page(GFP_ATOMIC|__GFP_COLD);
> - if (!page)
> - goto err;
> -
> - dst_offset = 0;
> - first = NULL;
> - while (dst_offset < PAGE_SIZE && slot < nr_slots) {
> - gop->flags = GNTCOPY_source_gref;
> -
> - gop->source.u.ref = txp->gref;
> - gop->source.domid = vif->domid;
> - gop->source.offset = txp->offset;
> -
> - gop->dest.domid = DOMID_SELF;
> -
> - gop->dest.offset = dst_offset;
> - gop->dest.u.gmfn =
> virt_to_mfn(page_address(page));
> -
> - if (dst_offset + txp->size > PAGE_SIZE) {
> - /* This page can only merge a portion
> - * of tx request. Do not increment any
> - * pointer / counter here. The txp
> - * will be dealt with in future
> - * rounds, eventually hitting the
> - * `else` branch.
> - */
> - gop->len = PAGE_SIZE - dst_offset;
> - txp->offset += gop->len;
> - txp->size -= gop->len;
> - dst_offset += gop->len; /* quit loop */
> - } else {
> - /* This tx request can be merged in the page
> */
> - gop->len = txp->size;
> - dst_offset += gop->len;
> -
> + for (shinfo->nr_frags = start; shinfo->nr_frags < nr_slots;
> + shinfo->nr_frags++, txp++, gop++) {
> index = pending_index(vif-
> >pending_cons++);
> -
> pending_idx = vif->pending_ring[index];
> -
> -
> memcpy(&pending_tx_info[pending_idx].req, txp,
> - sizeof(*txp));
> -
> - /* Poison these fields, corresponding
> - * fields for head tx req will be set
> - * to correct values after the loop.
> - */
> - vif->mmap_pages[pending_idx] = (void
> *)(~0UL);
> - pending_tx_info[pending_idx].head =
> - INVALID_PENDING_RING_IDX;
> -
> - if (!first) {
> - first =
> &pending_tx_info[pending_idx];
> - start_idx = index;
> - head_idx = pending_idx;
> - }
> -
> - txp++;
> - slot++;
> - }
> -
> - gop++;
> - }
> -
> - first->req.offset = 0;
> - first->req.size = dst_offset;
> - first->head = start_idx;
> - vif->mmap_pages[head_idx] = page;
> - frag_set_pending_idx(&frags[shinfo->nr_frags], head_idx);
> + xenvif_tx_create_gop(vif, pending_idx, txp, gop);
> + frag_set_pending_idx(&frags[shinfo->nr_frags],
> pending_idx);
> }
>
> BUG_ON(shinfo->nr_frags > MAX_SKB_FRAGS);
> @@ -1005,9 +934,9 @@ err:
>
> static int xenvif_tx_check_gop(struct xenvif *vif,
> struct sk_buff *skb,
> - struct gnttab_copy **gopp)
> + struct gnttab_map_grant_ref **gopp)
> {
> - struct gnttab_copy *gop = *gopp;
> + struct gnttab_map_grant_ref *gop = *gopp;
> u16 pending_idx = *((u16 *)skb->data);
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> struct pending_tx_info *tx_info;
> @@ -1019,6 +948,16 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
> err = gop->status;
> if (unlikely(err))
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_ERROR);
> + else {
> + if (vif->grant_tx_handle[pending_idx] !=
> + NETBACK_INVALID_HANDLE) {
> + netdev_err(vif->dev,
> + "Stale mapped handle! pending_idx %x
> handle %x\n",
> + pending_idx, vif-
> >grant_tx_handle[pending_idx]);
> + xenvif_fatal_tx_err(vif);
> + }
> + vif->grant_tx_handle[pending_idx] = gop->handle;
> + }
>
> /* Skip first skb fragment if it is on same page as header fragment. */
> start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
> @@ -1032,18 +971,24 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
> head = tx_info->head;
>
> /* Check error status: if okay then remember grant handle.
> */
> - do {
> newerr = (++gop)->status;
> - if (newerr)
> - break;
> - peek = vif->pending_ring[pending_index(++head)];
> - } while (!pending_tx_is_head(vif, peek));
>
> if (likely(!newerr)) {
> + if (vif->grant_tx_handle[pending_idx] !=
> + NETBACK_INVALID_HANDLE) {
> + netdev_err(vif->dev,
> + "Stale mapped handle! pending_idx
> %x handle %x\n",
> + pending_idx,
> + vif->grant_tx_handle[pending_idx]);
> + xenvif_fatal_tx_err(vif);
> + }
> + vif->grant_tx_handle[pending_idx] = gop->handle;
> /* Had a previous error? Invalidate this fragment. */
> - if (unlikely(err))
> + if (unlikely(err)) {
> + xenvif_idx_unmap(vif, pending_idx);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_OKAY);
> + }
> continue;
> }
>
> @@ -1056,9 +1001,11 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
>
> /* First error: invalidate header and preceding fragments. */
> pending_idx = *((u16 *)skb->data);
> + xenvif_idx_unmap(vif, pending_idx);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_OKAY);
> for (j = start; j < i; j++) {
> pending_idx = frag_get_pending_idx(&shinfo-
> >frags[j]);
> + xenvif_idx_unmap(vif, pending_idx);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_OKAY);
> }
> @@ -1071,7 +1018,8 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
> return err;
> }
>
> -static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
> +static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb,
> + u16 prev_pending_idx)
> {
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> int nr_frags = shinfo->nr_frags;
> @@ -1085,6 +1033,15 @@ static void xenvif_fill_frags(struct xenvif *vif,
> struct sk_buff *skb)
>
> pending_idx = frag_get_pending_idx(frag);
>
> + /* If this is not the first frag, chain it to the previous*/
> + vif->pending_tx_info[pending_idx].callback_struct.ctx =
> NULL;
> + if (pending_idx != prev_pending_idx) {
> + vif-
> >pending_tx_info[prev_pending_idx].callback_struct.ctx =
> + &(vif-
> >pending_tx_info[pending_idx].callback_struct);
> + prev_pending_idx = pending_idx;
> + }
> +
> +
> txp = &vif->pending_tx_info[pending_idx].req;
> page = virt_to_page(idx_to_kaddr(vif, pending_idx));
> __skb_fill_page_desc(skb, i, page, txp->offset, txp->size);
> @@ -1092,10 +1049,15 @@ static void xenvif_fill_frags(struct xenvif *vif,
> struct sk_buff *skb)
> skb->data_len += txp->size;
> skb->truesize += txp->size;
>
> - /* Take an extra reference to offset xenvif_idx_release */
> + /* Take an extra reference to offset network stack's
> put_page */
> get_page(vif->mmap_pages[pending_idx]);
> - xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_OKAY);
> }
> + /* FIXME: __skb_fill_page_desc set this to true because page-
> >pfmemalloc
> + * overlaps with "index", and "mapping" is not set. I think mapping
> + * should be set. If delivered to local stack, it would drop this
> + * skb in sk_filter unless the socket has the right to use it.
> + */
> + skb->pfmemalloc = false;
> }
>
> static int xenvif_get_extras(struct xenvif *vif,
> @@ -1426,7 +1388,7 @@ static bool tx_credit_exceeded(struct xenvif *vif,
> unsigned size)
>
> static unsigned xenvif_tx_build_gops(struct xenvif *vif)
> {
> - struct gnttab_copy *gop = vif->tx_copy_ops, *request_gop;
> + struct gnttab_map_grant_ref *gop = vif->tx_map_ops,
> *request_gop;
> struct sk_buff *skb;
> int ret;
>
> @@ -1533,30 +1495,10 @@ static unsigned xenvif_tx_build_gops(struct
> xenvif *vif)
> }
> }
>
> - /* XXX could copy straight to head */
> - page = xenvif_alloc_page(vif, pending_idx);
> - if (!page) {
> - kfree_skb(skb);
> - xenvif_tx_err(vif, &txreq, idx);
> - break;
> - }
> -
> - gop->source.u.ref = txreq.gref;
> - gop->source.domid = vif->domid;
> - gop->source.offset = txreq.offset;
> -
> - gop->dest.u.gmfn = virt_to_mfn(page_address(page));
> - gop->dest.domid = DOMID_SELF;
> - gop->dest.offset = txreq.offset;
> -
> - gop->len = txreq.size;
> - gop->flags = GNTCOPY_source_gref;
> + xenvif_tx_create_gop(vif, pending_idx, &txreq, gop);
>
> gop++;
>
> - memcpy(&vif->pending_tx_info[pending_idx].req,
> - &txreq, sizeof(txreq));
> - vif->pending_tx_info[pending_idx].head = index;
> *((u16 *)skb->data) = pending_idx;
>
> __skb_put(skb, data_len);
> @@ -1585,17 +1527,17 @@ static unsigned xenvif_tx_build_gops(struct
> xenvif *vif)
>
> vif->tx.req_cons = idx;
>
> - if ((gop-vif->tx_copy_ops) >= ARRAY_SIZE(vif-
> >tx_copy_ops))
> + if ((gop-vif->tx_map_ops) >= ARRAY_SIZE(vif-
> >tx_map_ops))
> break;
> }
>
> - return gop - vif->tx_copy_ops;
> + return gop - vif->tx_map_ops;
> }
>
>
> static int xenvif_tx_submit(struct xenvif *vif, int budget)
> {
> - struct gnttab_copy *gop = vif->tx_copy_ops;
> + struct gnttab_map_grant_ref *gop = vif->tx_map_ops;
> struct sk_buff *skb;
> int work_done = 0;
>
> @@ -1620,14 +1562,25 @@ static int xenvif_tx_submit(struct xenvif *vif, int
> budget)
> memcpy(skb->data,
> (void *)(idx_to_kaddr(vif, pending_idx)|txp->offset),
> data_len);
> + vif->pending_tx_info[pending_idx].callback_struct.ctx =
> NULL;
> if (data_len < txp->size) {
> /* Append the packet payload as a fragment. */
> txp->offset += data_len;
> txp->size -= data_len;
> - } else {
> + skb_shinfo(skb)->destructor_arg =
> + &vif-
> >pending_tx_info[pending_idx].callback_struct;
> + } else if (!skb_shinfo(skb)->nr_frags) {
> /* Schedule a response immediately. */
> + skb_shinfo(skb)->destructor_arg = NULL;
> + xenvif_idx_unmap(vif, pending_idx);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_OKAY);
> + } else {
> + /* FIXME: first request fits linear space, I don't know
> + * if any guest would do that, but I think it's possible
> + */

The Windows frontend, because it has to parse the packet headers, will coalesce everything up to the payload in a single frag and it would be a good idea to copy this directly into the linear area.

> + skb_shinfo(skb)->destructor_arg =
> + &vif-
> >pending_tx_info[pending_idx].callback_struct;
> }
>
> if (txp->flags & XEN_NETTXF_csum_blank)
> @@ -1635,13 +1588,19 @@ static int xenvif_tx_submit(struct xenvif *vif, int
> budget)
> else if (txp->flags & XEN_NETTXF_data_validated)
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> - xenvif_fill_frags(vif, skb);
> + xenvif_fill_frags(vif, skb, pending_idx);
>
> if (skb_is_nonlinear(skb) && skb_headlen(skb) <
> PKT_PROT_LEN) {
> int target = min_t(int, skb->len, PKT_PROT_LEN);
> __pskb_pull_tail(skb, target - skb_headlen(skb));
> }
>
> + /* Set this flag after __pskb_pull_tail, as it can trigger
> + * skb_copy_ubufs, while we are still in control of the skb
> + */

You can't be sure that there will be no subsequent pullups. The v6 parsing code I added may need to do that on a (hopefully) rare occasion.

Paul

> + if (skb_shinfo(skb)->destructor_arg)
> + skb_shinfo(skb)->tx_flags |=
> SKBTX_DEV_ZEROCOPY;
> +
> skb->dev = vif->dev;
> skb->protocol = eth_type_trans(skb, skb->dev);
> skb_reset_network_header(skb);
> @@ -1770,17 +1729,25 @@ static inline void xenvif_tx_action_dealloc(struct
> xenvif *vif)
> int xenvif_tx_action(struct xenvif *vif, int budget)
> {
> unsigned nr_gops;
> - int work_done;
> + int work_done, ret;
>
> if (unlikely(!tx_work_todo(vif)))
> return 0;
>
> + xenvif_tx_action_dealloc(vif);
> +
> nr_gops = xenvif_tx_build_gops(vif);
>
> if (nr_gops == 0)
> return 0;
>
> - gnttab_batch_copy(vif->tx_copy_ops, nr_gops);
> + if (nr_gops) {
> + ret = gnttab_map_refs(vif->tx_map_ops,
> + NULL,
> + vif->pages_to_gnt,
> + nr_gops);
> + BUG_ON(ret);
> + }
>
> work_done = xenvif_tx_submit(vif, nr_gops);
>
> @@ -1791,45 +1758,13 @@ static void xenvif_idx_release(struct xenvif *vif,
> u16 pending_idx,
> u8 status)
> {
> struct pending_tx_info *pending_tx_info;
> - pending_ring_idx_t head;
> + pending_ring_idx_t index;
> u16 peek; /* peek into next tx request */
>
> - BUG_ON(vif->mmap_pages[pending_idx] == (void *)(~0UL));
> -
> - /* Already complete? */
> - if (vif->mmap_pages[pending_idx] == NULL)
> - return;
> -
> - pending_tx_info = &vif->pending_tx_info[pending_idx];
> -
> - head = pending_tx_info->head;
> -
> - BUG_ON(!pending_tx_is_head(vif, head));
> - BUG_ON(vif->pending_ring[pending_index(head)] != pending_idx);
> -
> - do {
> - pending_ring_idx_t index;
> - pending_ring_idx_t idx = pending_index(head);
> - u16 info_idx = vif->pending_ring[idx];
> -
> - pending_tx_info = &vif->pending_tx_info[info_idx];
> + pending_tx_info = &vif->pending_tx_info[pending_idx];
> make_tx_response(vif, &pending_tx_info->req, status);
> -
> - /* Setting any number other than
> - * INVALID_PENDING_RING_IDX indicates this slot is
> - * starting a new packet / ending a previous packet.
> - */
> - pending_tx_info->head = 0;
> -
> index = pending_index(vif->pending_prod++);
> - vif->pending_ring[index] = vif->pending_ring[info_idx];
> -
> - peek = vif->pending_ring[pending_index(++head)];
> -
> - } while (!pending_tx_is_head(vif, peek));
> -
> - put_page(vif->mmap_pages[pending_idx]);
> - vif->mmap_pages[pending_idx] = NULL;
> + vif->pending_ring[index] = pending_idx;
> }
>
> void xenvif_idx_unmap(struct xenvif *vif, u16 pending_idx)
> @@ -1904,6 +1839,8 @@ static inline int rx_work_todo(struct xenvif *vif)
>
> static inline int tx_work_todo(struct xenvif *vif)
> {
> + if (vif->dealloc_cons != vif->dealloc_prod)
> + return 1;
>
> if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->tx)) &&
> (nr_pending_reqs(vif) + XEN_NETBK_LEGACY_SLOTS_MAX
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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