RE: [PATCH net-next v3 2/2] xen-netback: Grant copy the header instead of map and memcpy
From: Paul Durrant
Date: Thu Apr 03 2014 - 04:07:58 EST
> -----Original Message-----
> From: Zoltan Kiss
> Sent: 02 April 2014 18:05
> To: Ian Campbell; Wei Liu; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> Jonathan Davies; Zoltan Kiss
> Subject: [PATCH net-next v3 2/2] xen-netback: Grant copy the header
> instead of map and memcpy
>
> An old inefficiency of the TX path that we are grant mapping the first slot,
> and then copy the header part to the linear area. Instead, doing a grant copy
> for that header straight on is more reasonable. Especially because there are
> ongoing efforts to make Xen avoiding TLB flush after unmap when the page
> were
> not touched in Dom0. In the original way the memcpy ruined that.
> The key changes:
> - the vif has a tx_copy_ops array again
> - xenvif_tx_build_gops sets up the grant copy operations
> - we don't have to figure out whether the header and first frag are on the
> same
> grant mapped page or not
> Note, we only grant copy PKT_PROT_LEN bytes from the first slot, the rest (if
> any) will be on the first frag, which is grant mapped. If the first slot is
> smaller than PKT_PROT_LEN, then we grant copy that, and later
> __pskb_pull_tail
> will pull more from the frags (if any)
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
Looks good to me.
Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> v2:
> - extend commit message
> - add patch to rename map ops
>
> v3:
> - remove unrelated refactoring
> - remove stale newline
> - fix sanity check at the end of build_gops
> - change debug message in tx_submit
> - remove unnecessary 'else' from tx_action
>
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-
> netback/common.h
> index 89b2d42..c995532 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -119,6 +119,7 @@ struct xenvif {
> struct pending_tx_info pending_tx_info[MAX_PENDING_REQS];
> grant_handle_t grant_tx_handle[MAX_PENDING_REQS];
>
> + struct gnttab_copy tx_copy_ops[MAX_PENDING_REQS];
> struct gnttab_map_grant_ref tx_map_ops[MAX_PENDING_REQS];
> struct gnttab_unmap_grant_ref
> tx_unmap_ops[MAX_PENDING_REQS];
> /* passed to gnttab_[un]map_refs with pages under (un)mapping */
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> index 8ce93ff..a6cacf1 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -939,35 +939,37 @@ static inline void xenvif_grant_handle_reset(struct
> xenvif *vif,
>
> static int xenvif_tx_check_gop(struct xenvif *vif,
> struct sk_buff *skb,
> - struct gnttab_map_grant_ref **gopp_map)
> + struct gnttab_map_grant_ref **gopp_map,
> + struct gnttab_copy **gopp_copy)
> {
> struct gnttab_map_grant_ref *gop_map = *gopp_map;
> u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> - struct pending_tx_info *tx_info;
> int nr_frags = shinfo->nr_frags;
> - int i, err, start;
> + int i, err;
> struct sk_buff *first_skb = NULL;
>
> /* Check status of header. */
> - err = gop_map->status;
> - if (unlikely(err))
> + err = (*gopp_copy)->status;
> + (*gopp_copy)++;
> + if (unlikely(err)) {
> + if (net_ratelimit())
> + netdev_dbg(vif->dev,
> + "Grant copy of header failed! status: %d
> pending_idx% %u ref: %u\n",
> + (*gopp_copy)->status,
> + pending_idx,
> + (*gopp_copy)->source.u.ref);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_ERROR);
> - else
> - xenvif_grant_handle_set(vif, pending_idx , gop_map-
> >handle);
> -
> - /* Skip first skb fragment if it is on same page as header fragment. */
> - start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
> + }
>
> check_frags:
> - for (i = start; i < nr_frags; i++) {
> + for (i = 0; i < nr_frags; i++, gop_map++) {
> int j, newerr;
>
> pending_idx = frag_get_pending_idx(&shinfo->frags[i]);
> - tx_info = &vif->pending_tx_info[pending_idx];
>
> /* Check error status: if okay then remember grant handle.
> */
> - newerr = (++gop_map)->status;
> + newerr = gop_map->status;
>
> if (likely(!newerr)) {
> xenvif_grant_handle_set(vif,
> @@ -980,18 +982,20 @@ check_frags:
> }
>
> /* Error on this fragment: respond to client with an error. */
> + if (net_ratelimit())
> + netdev_dbg(vif->dev,
> + "Grant map of %d. frag failed! status: %d
> pending_idx% %u ref: %u\n",
> + i,
> + gop_map->status,
> + pending_idx,
> + gop_map->ref);
> xenvif_idx_release(vif, pending_idx,
> XEN_NETIF_RSP_ERROR);
>
> /* Not the first error? Preceding frags already invalidated. */
> if (err)
> continue;
> - /* First error: invalidate header and preceding fragments. */
> - if (!first_skb)
> - pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> - else
> - pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> - xenvif_idx_unmap(vif, pending_idx);
> - for (j = start; j < i; j++) {
> + /* First error: invalidate preceding fragments. */
> + for (j = 0; j < i; j++) {
> pending_idx = frag_get_pending_idx(&shinfo-
> >frags[j]);
> xenvif_idx_unmap(vif, pending_idx);
> }
> @@ -1005,7 +1009,6 @@ check_frags:
> skb = shinfo->frag_list;
> shinfo = skb_shinfo(skb);
> nr_frags = shinfo->nr_frags;
> - start = 0;
>
> goto check_frags;
> }
> @@ -1016,15 +1019,13 @@ check_frags:
> if (first_skb && err) {
> int j;
> shinfo = skb_shinfo(first_skb);
> - pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> - start = (frag_get_pending_idx(&shinfo->frags[0]) ==
> pending_idx);
> - for (j = start; j < shinfo->nr_frags; j++) {
> + for (j = 0; j < shinfo->nr_frags; j++) {
> pending_idx = frag_get_pending_idx(&shinfo-
> >frags[j]);
> xenvif_idx_unmap(vif, pending_idx);
> }
> }
>
> - *gopp_map = gop_map + 1;
> + *gopp_map = gop_map;
> return err;
> }
>
> @@ -1035,9 +1036,6 @@ static void xenvif_fill_frags(struct xenvif *vif, struct
> sk_buff *skb)
> int i;
> u16 prev_pending_idx = INVALID_PENDING_IDX;
>
> - if (skb_shinfo(skb)->destructor_arg)
> - prev_pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> -
> for (i = 0; i < nr_frags; i++) {
> skb_frag_t *frag = shinfo->frags + i;
> struct xen_netif_tx_request *txp;
> @@ -1047,10 +1045,10 @@ 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*/
> - if (unlikely(prev_pending_idx == INVALID_PENDING_IDX))
> + if (prev_pending_idx == INVALID_PENDING_IDX)
> skb_shinfo(skb)->destructor_arg =
> &callback_param(vif, pending_idx);
> - else if (likely(pending_idx != prev_pending_idx))
> + else
> callback_param(vif, prev_pending_idx).ctx =
> &callback_param(vif, pending_idx);
>
> @@ -1190,7 +1188,10 @@ static bool tx_credit_exceeded(struct xenvif *vif,
> unsigned size)
> return false;
> }
>
> -static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget)
> +static void xenvif_tx_build_gops(struct xenvif *vif,
> + int budget,
> + unsigned *copy_ops,
> + unsigned *map_ops)
> {
> struct gnttab_map_grant_ref *gop = vif->tx_map_ops,
> *request_gop;
> struct sk_buff *skb;
> @@ -1293,22 +1294,36 @@ static unsigned xenvif_tx_build_gops(struct
> xenvif *vif, int budget)
> }
> }
>
> - xenvif_tx_create_map_op(vif, pending_idx, &txreq, gop);
> -
> - gop++;
> -
> XENVIF_TX_CB(skb)->pending_idx = pending_idx;
>
> __skb_put(skb, data_len);
> + vif->tx_copy_ops[*copy_ops].source.u.ref = txreq.gref;
> + vif->tx_copy_ops[*copy_ops].source.domid = vif->domid;
> + vif->tx_copy_ops[*copy_ops].source.offset = txreq.offset;
> +
> + vif->tx_copy_ops[*copy_ops].dest.u.gmfn =
> + virt_to_mfn(skb->data);
> + vif->tx_copy_ops[*copy_ops].dest.domid = DOMID_SELF;
> + vif->tx_copy_ops[*copy_ops].dest.offset =
> + offset_in_page(skb->data);
> +
> + vif->tx_copy_ops[*copy_ops].len = data_len;
> + vif->tx_copy_ops[*copy_ops].flags =
> GNTCOPY_source_gref;
> +
> + (*copy_ops)++;
>
> skb_shinfo(skb)->nr_frags = ret;
> if (data_len < txreq.size) {
> skb_shinfo(skb)->nr_frags++;
> frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
> pending_idx);
> + xenvif_tx_create_map_op(vif, pending_idx, &txreq,
> gop);
> + gop++;
> } else {
> frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
> INVALID_PENDING_IDX);
> + memcpy(&vif->pending_tx_info[pending_idx].req,
> &txreq,
> + sizeof(txreq));
> }
>
> vif->pending_cons++;
> @@ -1325,11 +1340,13 @@ static unsigned xenvif_tx_build_gops(struct
> xenvif *vif, int budget)
>
> vif->tx.req_cons = idx;
>
> - if ((gop-vif->tx_map_ops) >= ARRAY_SIZE(vif-
> >tx_map_ops))
> + if (((gop-vif->tx_map_ops) >= ARRAY_SIZE(vif-
> >tx_map_ops)) ||
> + (*copy_ops >= ARRAY_SIZE(vif->tx_copy_ops)))
> break;
> }
>
> - return gop - vif->tx_map_ops;
> + (*map_ops) = gop - vif->tx_map_ops;
> + return;
> }
>
> /* Consolidate skb with a frag_list into a brand new one with local pages on
> @@ -1401,6 +1418,7 @@ static int xenvif_handle_frag_list(struct xenvif *vif,
> struct sk_buff *skb)
> static int xenvif_tx_submit(struct xenvif *vif)
> {
> struct gnttab_map_grant_ref *gop_map = vif->tx_map_ops;
> + struct gnttab_copy *gop_copy = vif->tx_copy_ops;
> struct sk_buff *skb;
> int work_done = 0;
>
> @@ -1413,27 +1431,22 @@ static int xenvif_tx_submit(struct xenvif *vif)
> txp = &vif->pending_tx_info[pending_idx].req;
>
> /* Check the remap error code. */
> - if (unlikely(xenvif_tx_check_gop(vif, skb, &gop_map))) {
> - netdev_dbg(vif->dev, "netback grant failed.\n");
> + if (unlikely(xenvif_tx_check_gop(vif, skb, &gop_map,
> &gop_copy))) {
> skb_shinfo(skb)->nr_frags = 0;
> kfree_skb(skb);
> continue;
> }
>
> data_len = skb->len;
> - memcpy(skb->data,
> - (void *)(idx_to_kaddr(vif, pending_idx)|txp->offset),
> - data_len);
> callback_param(vif, pending_idx).ctx = NULL;
> if (data_len < txp->size) {
> /* Append the packet payload as a fragment. */
> txp->offset += data_len;
> txp->size -= data_len;
> - skb_shinfo(skb)->destructor_arg =
> - &callback_param(vif, pending_idx);
> } else {
> /* Schedule a response immediately. */
> - xenvif_idx_unmap(vif, pending_idx);
> + xenvif_idx_release(vif, pending_idx,
> + XEN_NETIF_RSP_OKAY);
> }
>
> if (txp->flags & XEN_NETTXF_csum_blank)
> @@ -1612,22 +1625,25 @@ static inline void xenvif_tx_dealloc_action(struct
> xenvif *vif)
> /* Called after netfront has transmitted */
> int xenvif_tx_action(struct xenvif *vif, int budget)
> {
> - unsigned nr_mops;
> + unsigned nr_mops, nr_cops = 0;
> int work_done, ret;
>
> if (unlikely(!tx_work_todo(vif)))
> return 0;
>
> - nr_mops = xenvif_tx_build_gops(vif, budget);
> + xenvif_tx_build_gops(vif, budget, &nr_cops, &nr_mops);
>
> - if (nr_mops == 0)
> + if (nr_cops == 0)
> return 0;
>
> - ret = gnttab_map_refs(vif->tx_map_ops,
> - NULL,
> - vif->pages_to_map,
> - nr_mops);
> - BUG_ON(ret);
> + gnttab_batch_copy(vif->tx_copy_ops, nr_cops);
> + if (nr_mops != 0) {
> + ret = gnttab_map_refs(vif->tx_map_ops,
> + NULL,
> + vif->pages_to_map,
> + nr_mops);
> + BUG_ON(ret);
> + }
>
> work_done = xenvif_tx_submit(vif);
>
--
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