netdev - Re: [net-next 2/4] e1000: remove workaround for Errata 23 from jumbo alloc

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Date:	Thu, 17 May 2012 15:40:30 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
CC:	<davem@...emloft.net>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	<netdev@...r.kernel.org>, <gospo@...hat.com>, <sassmann@...hat.com>
Subject: Re: [net-next 2/4] e1000: remove workaround for Errata 23 from
 jumbo alloc

On Thu, 2012-05-17 at 04:27 -0700, Jeff Kirsher wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> According to the comment, errata 23 says that the memory we allocate
> can't cross a 64KiB boundary. In case of jumbo frames we allocate
> complete pages which can never cross the 64KiB boundary because
> PAGE_SIZE should be a multiple of 64KiB so we stop either before the

Should be a factor, not multiple.

[...]
> --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
> +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
> @@ -4391,30 +4391,6 @@ e1000_alloc_jumbo_rx_buffers(struct e1000_adapter *adapter,
>  			break;
>  		}
>  
> -		/* Fix for errata 23, can't cross 64kB boundary */
> -		if (!e1000_check_64k_bound(adapter, skb->data, bufsz)) {
> -			struct sk_buff *oldskb = skb;
> -			e_err(rx_err, "skb align check failed: %u bytes at "
> -			      "%p\n", bufsz, skb->data);
> -			/* Try again, without freeing the previous */
> -			skb = netdev_alloc_skb_ip_align(netdev, bufsz);
> -			/* Failed allocation, critical failure */
> -			if (!skb) {
> -				dev_kfree_skb(oldskb);
> -				adapter->alloc_rx_buff_failed++;
> -				break;
> -			}
> -
> -			if (!e1000_check_64k_bound(adapter, skb->data, bufsz)) {
> -				/* give up */
> -				dev_kfree_skb(skb);
> -				dev_kfree_skb(oldskb);
> -				break; /* while (cleaned_count--) */
> -			}
> -
> -			/* Use new allocation */
> -			dev_kfree_skb(oldskb);
> -		}
[...]

I don't believe PAGE_SIZE is >64K on any architecture, but perhaps you
should replace the run-time check with:

		BUILD_BUG_ON(PAGE_SIZE > 0x10000);

in case that changes in future.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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