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Re: [Xen-devel] [PATCHv1] xen-netfront: always keep the Rx ring full of requests

On 2014/10/2 9:33, David Vrabel wrote:
A full Rx ring only requires 1 MiB of memory.  This is not enough
memory that it is useful to dynamically scale the number of Rx
requests in the ring based on traffic rates.

Keeping the ring full of Rx requests handles bursty traffic better
than trying to converges on an optimal number of requests to keep

On a 4 core host, an iperf -P 64 -t 60 run from dom0 to a 4 VCPU guest
improved from 5.1 Gbit/s to 5.6 Gbit/s.  Gains with more bursty
traffic are expected to be higher.

Although removing sysfs is connected with the code change for full Rx ring utilization, I assume it is better to split this patch into two to make it simpler?

+ queue->rx.req_prod_pvt = req_prod;
+       /* Not enough requests? Try again later. */
+       if (req_prod - queue->rx.rsp_cons < NET_RX_SLOTS_MIN) {
+               mod_timer(&queue->rx_refill_timer, jiffies + (HZ/10));
+               return;

If the previous for loop breaks because of failure of xennet_alloc_one_rx_buffer, then notify_remote_via_irq is missed here if the code returns directly.

+       }

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