Re: [Xen-devel] [PATCH net-next v3 1/9] xen-netback: Introduce TX grant map definitions

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jan 08, 2014 at 12:10:10AM +0000, Zoltan Kiss wrote:
> This patch contains the new definitions necessary for grant mapping.
> 
> v2:
> - move unmapping to separate thread. The NAPI instance has to be scheduled
>   even from thread context, which can cause huge delays
> - that causes unfortunately bigger struct xenvif
> - store grant handle after checking validity
> 
> v3:
> - fix comment in xenvif_tx_dealloc_action()
> - call unmap hypercall directly instead of gnttab_unmap_refs(), which does
>   unnecessary m2p_override. Also remove pages_to_[un]map members

Is it worthy to have another function call
gnttab_unmap_refs_no_m2p_override in Xen core driver, or just add a
parameter to control wether we need to touch m2p_override? I *think* it
will benefit block driver as well?

(CC Roger and David for input)

> - BUG() if grant_tx_handle corrupted
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> 
> ---
[...]
>  
>  #define XENVIF_QUEUE_LENGTH 32
>  #define XENVIF_NAPI_WEIGHT  64
> diff --git a/drivers/net/xen-netback/netback.c 
> b/drivers/net/xen-netback/netback.c
> index addfe1d1..7c241f9 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -771,6 +771,19 @@ static struct page *xenvif_alloc_page(struct xenvif *vif,
>       return page;
>  }
>  
> +static inline void xenvif_tx_create_gop(struct xenvif *vif, u16 pending_idx,
> +            struct xen_netif_tx_request *txp,
> +            struct gnttab_map_grant_ref *gop)

Indentation.

> +{
> +     gnttab_set_map_op(gop, idx_to_kaddr(vif, pending_idx),
> +                       GNTMAP_host_map | GNTMAP_readonly,
> +                       txp->gref, vif->domid);
> +
> +     memcpy(&vif->pending_tx_info[pending_idx].req, txp,
> +            sizeof(*txp));
> +
> +}
> +
[...]
> +void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success)
> +{
> +     unsigned long flags;
> +     pending_ring_idx_t index;
> +     u16 pending_idx = ubuf->desc;
> +     struct pending_tx_info *temp =
> +             container_of(ubuf, struct pending_tx_info, callback_struct);
> +     struct xenvif *vif =
> +             container_of(temp - pending_idx, struct xenvif,
> +                     pending_tx_info[0]);

Indentation.

> +
> +     spin_lock_irqsave(&vif->dealloc_lock, flags);
> +     do {
> +             pending_idx = ubuf->desc;
> +             ubuf = (struct ubuf_info *) ubuf->ctx;
> +             index = pending_index(vif->dealloc_prod);
> +             vif->dealloc_ring[index] = pending_idx;
> +             /* Sync with xenvif_tx_action_dealloc:

xenvif_tx_dealloc_action I suppose.

> +              * insert idx then incr producer.
> +              */
> +             smp_wmb();
> +             vif->dealloc_prod++;
> +     } while (ubuf);
> +     wake_up(&vif->dealloc_wq);
> +     spin_unlock_irqrestore(&vif->dealloc_lock, flags);
> +}
> +
> +static inline void xenvif_tx_dealloc_action(struct xenvif *vif)
> +{
> +     struct gnttab_unmap_grant_ref *gop;
> +     pending_ring_idx_t dc, dp;
> +     u16 pending_idx, pending_idx_release[MAX_PENDING_REQS];
> +     unsigned int i = 0;
> +
> +     dc = vif->dealloc_cons;
> +     gop = vif->tx_unmap_ops;
> +
> +     /* Free up any grants we have finished using */
> +     do {
> +             dp = vif->dealloc_prod;
> +
> +             /* Ensure we see all indices enqueued by all
> +              * xenvif_zerocopy_callback().
> +              */
> +             smp_rmb();
> +
> +             while (dc != dp) {
> +                     pending_idx =
> +                             vif->dealloc_ring[pending_index(dc++)];
> +
> +                     /* Already unmapped? */
> +                     if (vif->grant_tx_handle[pending_idx] ==
> +                             NETBACK_INVALID_HANDLE) {
> +                             netdev_err(vif->dev,
> +                                     "Trying to unmap invalid handle! "
> +                                     "pending_idx: %x\n", pending_idx);
> +                             continue;

You seemed to miss the BUG_ON we discussed?

See thread starting <52AF1A84.3090304@xxxxxxxxxx>.

Wei.

> +                     }
> +
> +                     pending_idx_release[gop-vif->tx_unmap_ops] =
> +                             pending_idx;
> +                     gnttab_set_unmap_op(gop,
> +                                     idx_to_kaddr(vif, pending_idx),
> +                                     GNTMAP_host_map,
> +                                     vif->grant_tx_handle[pending_idx]);
> +                     vif->grant_tx_handle[pending_idx] =
> +                             NETBACK_INVALID_HANDLE;
> +                     ++gop;
> +             }
> +


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