From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCHv1 net] xen-netback: require fewer guest Rx slots when not using GSO Date: Wed, 09 Sep 2015 12:34:59 -0700 (PDT) Message-ID: <20150909.123459.1956039261743477106.davem@davemloft.net> References: <1441718714-3256-1-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, xen-devel@lists.xenproject.org, ian.campbell@citrix.com, wei.liu2@citrix.com To: david.vrabel@citrix.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:34322 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751808AbbIITfA (ORCPT ); Wed, 9 Sep 2015 15:35:00 -0400 In-Reply-To: <1441718714-3256-1-git-send-email-david.vrabel@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: From: David Vrabel 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 Applied, thanks David.