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Message-ID: <20140109153015.GF12164@zion.uk.xensource.com>
Date: Thu, 9 Jan 2014 15:30:15 +0000
From: Wei Liu <wei.liu2@...rix.com>
To: Zoltan Kiss <zoltan.kiss@...rix.com>
CC: <ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next v3 2/9] xen-netback: Change TX path from grant
copy to mapping
On Wed, Jan 08, 2014 at 12:10:11AM +0000, Zoltan Kiss wrote:
> This patch changes the grant copy on the TX patch to grant mapping
>
> v2:
> - delete branch for handling fragmented packets fit PKT_PROT_LEN sized first
> request
> - mark the effect of using ballooned pages in a comment
> - place setting of skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY right
> before netif_receive_skb, and mark the importance of it
> - grab dealloc_lock before __napi_complete to avoid contention with the
> callback's napi_schedule
> - handle fragmented packets where first request < PKT_PROT_LEN
> - fix up error path when checksum_setup failed
> - check before teardown for pending grants, and start complain if they are
> there after 10 second
>
> v3:
> - delete a surplus checking from tx_action
> - remove stray line
> - squash xenvif_idx_unmap changes into the first patch
> - init spinlocks
> - call map hypercall directly instead of gnttab_map_refs()
I suppose this is to avoid touching m2p override as well, just as
previous patch uses unmap hypercall directly.
> - fix unmapping timeout in xenvif_free()
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>
> ---
> drivers/net/xen-netback/interface.c | 57 +++++++-
> drivers/net/xen-netback/netback.c | 251 ++++++++++++++---------------------
> 2 files changed, 153 insertions(+), 155 deletions(-)
>
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 7170f97..3b2b249 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -122,7 +122,9 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
> BUG_ON(skb->dev != dev);
>
> /* Drop the packet if vif is not ready */
> - if (vif->task == NULL || !xenvif_schedulable(vif))
> + if (vif->task == NULL ||
> + vif->dealloc_task == NULL ||
> + !xenvif_schedulable(vif))
Indentation.
> goto drop;
>
> /* At best we'll need one slot for the header and one for each
> @@ -345,8 +347,26 @@ 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;
> + spin_lock_init(&vif->dealloc_lock);
> + spin_lock_init(&vif->response_lock);
> + /* If ballooning is disabled, this will consume real memory, so you
> + * better enable it. The long term solution would be to use just a
> + * bunch of valid page descriptors, without dependency on ballooning
> + */
> + err = alloc_xenballooned_pages(MAX_PENDING_REQS,
> + vif->mmap_pages,
> + false);
Ditto.
> + 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
> @@ -390,6 +410,7 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
> goto err;
>
> init_waitqueue_head(&vif->wq);
> + init_waitqueue_head(&vif->dealloc_wq);
>
> if (tx_evtchn == rx_evtchn) {
> /* feature-split-event-channels == 0 */
> @@ -431,6 +452,14 @@ int xenvif_connect(struct xenvif *vif, unsigned long tx_ring_ref,
> goto err_rx_unbind;
> }
>
> + vif->dealloc_task = kthread_create(xenvif_dealloc_kthread,
> + (void *)vif, "%s-dealloc", vif->dev->name);
Ditto.
> + if (IS_ERR(vif->dealloc_task)) {
> + pr_warn("Could not allocate kthread for %s\n", vif->dev->name);
> + err = PTR_ERR(vif->dealloc_task);
> + goto err_rx_unbind;
> + }
> +
> vif->task = task;
>
> rtnl_lock();
[...]
>
> 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;
> @@ -920,6 +852,18 @@ 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]);
> + BUG();
> + }
> + set_phys_to_machine(idx_to_pfn(vif, pending_idx),
> + FOREIGN_FRAME(gop->dev_bus_addr >> PAGE_SHIFT));
What happens when you don't have this?
> + 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);
> @@ -933,18 +877,26 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
> head = tx_info->head;
>
[...]
> }
> @@ -1567,7 +1523,11 @@ static int xenvif_tx_submit(struct xenvif *vif)
> else if (txp->flags & XEN_NETTXF_data_validated)
> skb->ip_summed = CHECKSUM_UNNECESSARY;
>
> - xenvif_fill_frags(vif, skb);
> + xenvif_fill_frags(vif,
> + skb,
> + skb_shinfo(skb)->destructor_arg ?
> + pending_idx :
> + INVALID_PENDING_IDX);
>
Indentation.
> if (skb_is_nonlinear(skb) && skb_headlen(skb) < PKT_PROT_LEN) {
> int target = min_t(int, skb->len, PKT_PROT_LEN);
> @@ -1581,6 +1541,8 @@ static int xenvif_tx_submit(struct xenvif *vif)
> if (checksum_setup(vif, skb)) {
> netdev_dbg(vif->dev,
> "Can't setup checksum in net_tx_action\n");
> + if (skb_shinfo(skb)->destructor_arg)
> + skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
Do you still care setting the flag even if this skb is not going to be
delivered? If so can you state clearly the reason just like the
following hunk?
> kfree_skb(skb);
> continue;
> }
> @@ -1606,6 +1568,14 @@ static int xenvif_tx_submit(struct xenvif *vif)
>
> work_done++;
>
> + /* Set this flag right before netif_receive_skb, otherwise
> + * someone might think this packet already left netback, and
> + * do a skb_copy_ubufs while we are still in control of the
> + * skb. E.g. the __pskb_pull_tail earlier can do such thing.
> + */
> + if (skb_shinfo(skb)->destructor_arg)
> + skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> +
> netif_receive_skb(skb);
> }
>
> @@ -1715,7 +1685,7 @@ static inline void xenvif_tx_dealloc_action(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;
> @@ -1725,7 +1695,10 @@ int xenvif_tx_action(struct xenvif *vif, int budget)
> if (nr_gops == 0)
> return 0;
>
> - gnttab_batch_copy(vif->tx_copy_ops, nr_gops);
> + ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
> + vif->tx_map_ops,
> + nr_gops);
Why do you need to replace gnttab_batch_copy with hypercall? In the
ideal situation gnttab_batch_copy should behave the same as directly
hypercall but it also handles GNTST_eagain for you.
Wei.
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