Re: [Xen-devel] [PATCH net-next v4 2/9] xen-netback: Change TX path from grant copy to mapping

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jan 14, 2014 at 08:39:48PM +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()
> - fix unmapping timeout in xenvif_free()
> 
> v4:
> - fix indentations and comments
> - handle errors of set_phys_to_machine

There's no call to set_phys_to_machine in this patch. Did I miss
something?

> - go back to gnttab_map_refs instead of direct hypercall. Now we rely on the
>   modified API
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> ---
>  drivers/net/xen-netback/interface.c |   60 +++++++-
>  drivers/net/xen-netback/netback.c   |  256 
> ++++++++++++++---------------------
>  2 files changed, 159 insertions(+), 157 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/interface.c 
> b/drivers/net/xen-netback/interface.c
> index a7855b3..1e0bf71 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -123,7 +123,9 @@ 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))
>               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,

At the beginning of the function there's BUG_ON checks for vif->task. I
would suggest you do the same for vif->dealloc_task, just to be
consistent.

>       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);
> +     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 +452,16 @@ 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);
> +     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;

Please move this line before the above hunk. Don't separate it from
corresponding kthread_create.

Last but not least, though I've looked at this patch for several rounds
and and the basic logic looks correct to me, I would like it to go
through XenRT tests if possible -- eye inspection is error-prone to such
complicated change. (If I'm not mistaken you once told me you've done
regression tests already. That would be neat!)

Wei.

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