Re: [Xen-devel] [PATCH 2/4] xen/netback: Split one page pool into two(tx/rx) page pool.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-11-15 at 07:04 +0000, Annie Li wrote:
> For tx path, this implementation simplifies the work of searching out
> grant page from page pool based on grant reference.

It's still a linear search though, and it doesn't look much simpler to
me:
        for (i = 0; i < count; i++) {
                if (tx_pool)
                        vif = netbk->gnttab_tx_vif[i];
                else
                        vif = netbk->gnttab_rx_vif[i];

                pers_entry = vif->persistent_gnt;
                gnt_count = &vif->persistent_gntcnt;
                gnt_total = MAXIMUM_OUTSTANDING_BLOCK_REQS;
becomes:
        for (i = 0; i < count; i++) {
                if (tx_pool) {
                        vif = netbk->gnttab_tx_vif[i];
                        gnt_count = &vif->persistent_tx_gntcnt;
                        gnt_total = XEN_NETIF_TX_RING_SIZE;
                        pers_entry = vif->persistent_tx_gnt;
                } else {
                        vif = netbk->gnttab_rx_vif[i];
                        gnt_count = &vif->persistent_rx_gntcnt;
                        gnt_total = 2*XEN_NETIF_RX_RING_SIZE;
                        pers_entry = vif->persistent_rx_gnt;
                }

> @@ -111,8 +109,16 @@ struct xenvif {
>  
>       wait_queue_head_t waiting_to_free;
>  
> -     struct persistent_entry *persistent_gnt[MAXIMUM_OUTSTANDING_BLOCK_REQS];
> -     unsigned int persistent_gntcnt;
> +     struct persistent_entry *persistent_tx_gnt[XEN_NETIF_TX_RING_SIZE];
> +
> +     /*
> +      * 2*XEN_NETIF_RX_RING_SIZE is for the case of each head/fragment page

Shouldn't that been incorporated into MAXIMUM_OUTSTANDING_BLOCK_REQS
(sic) too?

> +      * using 2 copy operations.
> +      */
> +     struct persistent_entry *persistent_rx_gnt[2*XEN_NETIF_RX_RING_SIZE];

What is the per-vif memory overhead after this change?

Ian.


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