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Date: Wed, 09 Sep 2015 12:34:59 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: david.vrabel@...rix.com
Cc: netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
ian.campbell@...rix.com, wei.liu2@...rix.com
Subject: Re: [PATCHv1 net] xen-netback: require fewer guest Rx slots when
not using GSO
From: David Vrabel <david.vrabel@...rix.com>
Date: Tue, 8 Sep 2015 14:25:14 +0100
> Commit f48da8b14d04ca87ffcffe68829afd45f926ec6a (xen-netback: fix
> unlimited guest Rx internal queue and carrier flapping) introduced a
> regression.
>
> The PV frontend in IPXE only places 4 requests on the guest Rx ring.
> Since netback required at least (MAX_SKB_FRAGS + 1) slots, IPXE could
> not receive any packets.
>
> a) If GSO is not enabled on the VIF, fewer guest Rx slots are required
> for the largest possible packet. Calculate the required slots
> based on the maximum GSO size or the MTU.
>
> This calculation of the number of required slots relies on
> 1650d5455bd2 (xen-netback: always fully coalesce guest Rx packets)
> which present in 4.0-rc1 and later.
>
> b) Reduce the Rx stall detection to checking for at least one
> available Rx request. This is fine since we're predominately
> concerned with detecting interfaces which are down and thus have
> zero available Rx requests.
>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Applied, thanks David.
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