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

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Message-ID: <538F3E6A.7000002@citrix.com>
Date:	Wed, 4 Jun 2014 16:42:34 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>, <ian.campbell@...rix.com>,
	<wei.liu2@...rix.com>, <paul.durrant@...rix.com>,
	<linux@...elenboom.it>, <netdev@...r.kernel.org>,
	<david.vrabel@...rix.com>, <davem@...emloft.net>
Subject: Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring
 too many slots

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

Zoli
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