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Message-ID: <20121121151625.GA13127@konrad-lan.dumpdata.com>
Date: Wed, 21 Nov 2012 10:16:27 -0500
From: Konrad Rzeszutek Wilk <konrad@...nel.org>
To: Ian Campbell <ian.campbell@...rix.com>, davem@...emloft.net
Cc: netdev@...r.kernel.org, xen-devel@...ts.xen.org,
Eric Dumazet <edumazet@...gle.com>,
ANNIE LI <annie.li@...cle.com>,
Sander Eikelenboom <linux@...elenboom.it>,
Stefan Bader <stefan.bader@...onical.com>
Subject: Re: [PATCH V3] xen/netfront: handle compound page fragments on
transmit
On Wed, Nov 21, 2012 at 12:02:16PM +0000, Ian Campbell wrote:
> An SKB paged fragment can consist of a compound page with order > 0.
> However the netchannel protocol deals only in PAGE_SIZE frames.
>
> Handle this in xennet_make_frags by iterating over the frames which
> make up the page.
>
> This is the netfront equivalent to 6a8ed462f16b for netback.
>
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Cc: netdev@...r.kernel.org
> Cc: xen-devel@...ts.xen.org
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Konrad Rzeszutek Wilk <konrad@...nel.org>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
David, would you like me to send it to Linus via my tree or are you
OK sending him a git pull with this patch (and hopefully some other
ones?)
Thank you.
> Cc: ANNIE LI <annie.li@...cle.com>
> Cc: Sander Eikelenboom <linux@...elenboom.it>
> Cc: Stefan Bader <stefan.bader@...onical.com>
> ---
> v3: limit to 80-characters. Use net_alert_ratelimited.
> v2: check we have enough room in the ring and that the other end can
> cope with the number of slots in a single frame
> ---
> drivers/net/xen-netfront.c | 98 ++++++++++++++++++++++++++++++++++---------
> 1 files changed, 77 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..fc24eb9 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -452,29 +452,85 @@ static void xennet_make_frags(struct sk_buff *skb, struct net_device *dev,
> /* Grant backend access to each skb fragment page. */
> for (i = 0; i < frags; i++) {
> skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> + struct page *page = skb_frag_page(frag);
>
> - tx->flags |= XEN_NETTXF_more_data;
> + len = skb_frag_size(frag);
> + offset = frag->page_offset;
>
> - id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> - np->tx_skbs[id].skb = skb_get(skb);
> - tx = RING_GET_REQUEST(&np->tx, prod++);
> - tx->id = id;
> - ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> - BUG_ON((signed short)ref < 0);
> + /* Data must not cross a page boundary. */
> + BUG_ON(len + offset > PAGE_SIZE<<compound_order(page));
>
> - mfn = pfn_to_mfn(page_to_pfn(skb_frag_page(frag)));
> - gnttab_grant_foreign_access_ref(ref, np->xbdev->otherend_id,
> - mfn, GNTMAP_readonly);
> + /* Skip unused frames from start of page */
> + page += offset >> PAGE_SHIFT;
> + offset &= ~PAGE_MASK;
>
> - tx->gref = np->grant_tx_ref[id] = ref;
> - tx->offset = frag->page_offset;
> - tx->size = skb_frag_size(frag);
> - tx->flags = 0;
> + while (len > 0) {
> + unsigned long bytes;
> +
> + BUG_ON(offset >= PAGE_SIZE);
> +
> + bytes = PAGE_SIZE - offset;
> + if (bytes > len)
> + bytes = len;
> +
> + tx->flags |= XEN_NETTXF_more_data;
> +
> + id = get_id_from_freelist(&np->tx_skb_freelist,
> + np->tx_skbs);
> + np->tx_skbs[id].skb = skb_get(skb);
> + tx = RING_GET_REQUEST(&np->tx, prod++);
> + tx->id = id;
> + ref = gnttab_claim_grant_reference(&np->gref_tx_head);
> + BUG_ON((signed short)ref < 0);
> +
> + mfn = pfn_to_mfn(page_to_pfn(page));
> + gnttab_grant_foreign_access_ref(ref,
> + np->xbdev->otherend_id,
> + mfn, GNTMAP_readonly);
> +
> + tx->gref = np->grant_tx_ref[id] = ref;
> + tx->offset = offset;
> + tx->size = bytes;
> + tx->flags = 0;
> +
> + offset += bytes;
> + len -= bytes;
> +
> + /* Next frame */
> + if (offset == PAGE_SIZE && len) {
> + BUG_ON(!PageCompound(page));
> + page++;
> + offset = 0;
> + }
> + }
> }
>
> np->tx.req_prod_pvt = prod;
> }
>
> +/*
> + * Count how many ring slots are required to send the frags of this
> + * skb. Each frag might be a compound page.
> + */
> +static int xennet_count_skb_frag_slots(struct sk_buff *skb)
> +{
> + int i, frags = skb_shinfo(skb)->nr_frags;
> + int pages = 0;
> +
> + for (i = 0; i < frags; i++) {
> + skb_frag_t *frag = skb_shinfo(skb)->frags + i;
> + unsigned long size = skb_frag_size(frag);
> + unsigned long offset = frag->page_offset;
> +
> + /* Skip unused frames from start of page */
> + offset &= ~PAGE_MASK;
> +
> + pages += PFN_UP(offset + size);
> + }
> +
> + return pages;
> +}
> +
> static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> unsigned short id;
> @@ -487,23 +543,23 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
> grant_ref_t ref;
> unsigned long mfn;
> int notify;
> - int frags = skb_shinfo(skb)->nr_frags;
> + int slots;
> unsigned int offset = offset_in_page(data);
> unsigned int len = skb_headlen(skb);
> unsigned long flags;
>
> - frags += DIV_ROUND_UP(offset + len, PAGE_SIZE);
> - if (unlikely(frags > MAX_SKB_FRAGS + 1)) {
> - printk(KERN_ALERT "xennet: skb rides the rocket: %d frags\n",
> - frags);
> - dump_stack();
> + slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
> + xennet_count_skb_frag_slots(skb);
> + if (unlikely(slots > MAX_SKB_FRAGS + 1)) {
> + net_alert_ratelimited(
> + "xennet: skb rides the rocket: %d slots\n", slots);
> goto drop;
> }
>
> spin_lock_irqsave(&np->tx_lock, flags);
>
> if (unlikely(!netif_carrier_ok(dev) ||
> - (frags > 1 && !xennet_can_sg(dev)) ||
> + (slots > 1 && !xennet_can_sg(dev)) ||
> netif_needs_gso(skb, netif_skb_features(skb)))) {
> spin_unlock_irqrestore(&np->tx_lock, flags);
> goto drop;
> --
> 1.7.2.5
>
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