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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH net-next v2 2/2] xen-netback: Grant copy the header instead of map and memcpy
> -----Original Message-----
> From: Zoltan Kiss
> Sent: 31 March 2014 16:09
> To: Ian Campbell; Wei Liu; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> Jonathan Davies; Zoltan Kiss
> Subject: [PATCH net-next v2 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)
>
> Unrelated, but I've made a small refactoring in xenvif_get_extras as well.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> ---
> v2:
> - extend commit message
> - add patch to rename map ops
>
> 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 e781366..ba11ff5 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -915,35 +915,30 @@ 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;
> + err = (*gopp_copy)->status;
> + (*gopp_copy)++;
I guess there's no undo work in the case of a copy op so you can bump the copy
count here, but it might have been nicer to pair it with the update to the map
count.
> if (unlikely(err))
> 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,
> @@ -961,13 +956,8 @@ check_frags:
> /* 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);
> }
> @@ -981,7 +971,6 @@ check_frags:
> skb = shinfo->frag_list;
> shinfo = skb_shinfo(skb);
> nr_frags = shinfo->nr_frags;
> - start = 0;
>
> goto check_frags;
> }
> @@ -992,15 +981,13 @@ 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;
> }
>
> @@ -1011,9 +998,6 @@ 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;
> @@ -1023,10 +1007,10 @@ 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);
>
> @@ -1067,9 +1051,9 @@ static int xenvif_get_extras(struct xenvif *vif,
>
> memcpy(&extra, RING_GET_REQUEST(&vif->tx, cons),
> sizeof(extra));
> + vif->tx.req_cons = ++cons;
> if (unlikely(!extra.type ||
> extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
> - vif->tx.req_cons = ++cons;
> netdev_err(vif->dev,
> "Invalid extra type: %d\n", extra.type);
> xenvif_fatal_tx_err(vif);
> @@ -1077,7 +1061,6 @@ static int xenvif_get_extras(struct xenvif *vif,
> }
>
> memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
> - vif->tx.req_cons = ++cons;
I know you called this out as unrelated, but I still think it would be better
in a separate patch.
> } while (extra.flags & XEN_NETIF_EXTRA_FLAG_MORE);
>
> return work_to_do;
> @@ -1166,7 +1149,10 @@ 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;
> @@ -1269,24 +1255,39 @@ static unsigned xenvif_tx_build_gops(struct
> xenvif *vif, int budget)
> }
> }
>
> - xenvif_tx_create_gop(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_gop(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));
> }
>
> +
Unnecessary whitespace change.
> vif->pending_cons++;
>
> request_gop = xenvif_get_requests(vif, skb, txfrags, gop);
> @@ -1301,11 +1302,13 @@ 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_map_ops)))
Do you mean ARRAY_SIZE(vif->tx_copy_ops) here?
> 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
> @@ -1377,6 +1380,7 @@ 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;
>
> @@ -1389,7 +1393,7 @@ 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))) {
> + if (unlikely(xenvif_tx_check_gop(vif, skb, &gop_map,
> &gop_copy))) {
> netdev_dbg(vif->dev, "netback grant failed.\n");
It could have been the copy that failed. You should probably change the error
message.
> skb_shinfo(skb)->nr_frags = 0;
> kfree_skb(skb);
> @@ -1397,19 +1401,15 @@ static int xenvif_tx_submit(struct xenvif *vif)
> }
>
> 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)
> @@ -1588,22 +1588,26 @@ 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);
> + else {
Do you need an 'else' here? Unless I'm misreading the diff your previous clause
returns.
Paul
> + 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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