xen-netback: require fewer guest Rx slots when not using GSO

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Commit f48da8b14d (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
   1650d5455b (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@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

...

This commit is contained in:

David Vrabel 2015-09-08 14:25:14 +01:00 • committed by David S. Miller

parent 9b57ab8b58

commit 1d5d485239

2 changed files with 16 additions and 17 deletions

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10

drivers/net/xen-netback/common.h

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23

drivers/net/xen-netback/netback.c

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