netdev - Re: [PATCH net-next 2/3] virtio-net: use per-receive queue page frag alloc for mergeable bufs

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Message-ID: <52CDC03C.8070509@hp.com>
Date:	Wed, 08 Jan 2014 13:16:44 -0800
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Michael Dalton <mwdalton@...gle.com>,
	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	lf-virt <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH net-next 2/3] virtio-net: use per-receive queue page frag
 alloc for mergeable bufs

On 01/08/2014 10:09 AM, Eric Dumazet wrote:
> In normal networking land, when a host A sends frames to host B,
> nothing prevents A to pause the traffic to B if B is dropping packets
> under stress.
>
> A physical NIC do not use a workqueue to refill its RX queue but uses
> the following strategy :
>
> 0) Pre filling of RX ring buffer with N frames. This can use GFP_KERNEL
>     allocations with all needed (sleep/retry/shout) logic...
> 1) IRQ is handled.
> 2) Can we allocate a new buffer (GFP_ATOMIC) ?
>     If yes, we accept the frame,
>        and post the new buffer for the 'next frame'
>     If no, we drop the frame and recycle the memory for next round.

          and increment a suitably specific statistic so someone trying 
to diagnose performance/other problems can know we dropped the frame.

rick jones
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