netdev - Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

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Date:	Wed, 04 Jun 2014 11:59:45 -0400
From:	annie li <annie.li@...cle.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	wei.liu2@...rix.com, ian.campbell@...rix.com,
	netdev@...r.kernel.org, linux@...elenboom.it,
	paul.durrant@...rix.com, david.vrabel@...rix.com,
	xen-devel@...ts.xenproject.org, davem@...emloft.net
Subject: Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring
 too many slots


On 2014/6/4 11:42, Zoltan Kiss wrote:
> On 04/06/14 16:09, annie li wrote:
>>
>> On 2014/6/3 16:30, Zoltan Kiss wrote:
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots 
>>> than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,
>>
>> (XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?
>
> Do you think about the GSO slot? That's why I wrote "data slot", 
> however that's probably not a clear terminology.

What I mean is: XEN_NETIF_MAX_TX_SIZE is 0xFFFF, and 
XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE turns out to be 15 slots when 
PAGE_SIZE is 4096. You was trying to use XEN_NETIF_MAX_TX_SIZE as max 
size of packet - 64k?

> I'll add then that excluding GSO slot, as it doesn't carry data 
> directly, therefore it's irrelevant from this point of view.

Correct.:-)

Thanks
Annie
>
> Zoli
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel

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