netdev - Re: [PATCH 2.6.35-rc1] net: vmxnet3 fixes [1/5] Spare skb to avoid starvation

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Date:	Wed, 7 Jul 2010 10:46:39 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Shreyas Bhatewara <sbhatewara@...are.com>
Cc:	netdev@...r.kernel.org, pv-drivers@...are.com
Subject: Re: [PATCH 2.6.35-rc1] net: vmxnet3 fixes [1/5] Spare skb to avoid
 starvation

On Wed, 7 Jul 2010 02:21:55 -0700 (PDT)
Shreyas Bhatewara <sbhatewara@...are.com> wrote:

> 
> 
> From: Shreyas Bhatewara <sbhatewara@...are.com>
> 
> skb_alloc() failure can cause the recv ring to loose all packet reception.
> Avoid this by introducing a spare buffer.
> 
> Signed-off-by: Michael Stolarchuk <stolarchuk@...are.com>
> Signed-off-by: Shreyas Bhatewara <sbhatewara@...are.com>
> 

I don't see how this fixes the problem, what happens when
the spare buffer is used up? Better to design a flow control algorithm
that holds off sender if allocation fails, and retry allocation later
(for example with a work queue).

> diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
> index 989b742..5a50d10 100644
...

>  /*
> @@ -149,6 +149,13 @@ vmxnet3_cmd_ring_desc_avail(struct vmxnet3_cmd_ring *ring)
>  		ring->next2comp - ring->next2fill - 1;
>  }
>  
> +static inline bool
> +vmxnet3_cmd_ring_desc_empty(struct vmxnet3_cmd_ring *ring)
> +{
> +	return (ring->next2comp == ring->next2fill);
> +}

const is good practice on functions like this.

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