From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Durrant Subject: [PATCH net 2/3] xen-netback: worse-case estimate in xenvif_rx_action is underestimating Date: Thu, 27 Mar 2014 12:23:07 +0000 Message-ID: <1395922988-37702-3-git-send-email-paul.durrant@citrix.com> References: <1395922988-37702-1-git-send-email-paul.durrant@citrix.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Paul Durrant , Ian Campbell , Wei Liu , Sander Eikelenboom To: , Return-path: Received: from smtp02.citrix.com ([66.165.176.63]:7634 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755443AbaC0MXX (ORCPT ); Thu, 27 Mar 2014 08:23:23 -0400 In-Reply-To: <1395922988-37702-1-git-send-email-paul.durrant@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: The worse-case estimate for skb ring slot usage in xenvif_rx_action() fails to take fragment page_offset into account. The page_offset does, however, affect the number of times the fragmentation code calls start_new_rx_buffer() (i.e. consume another slot) and the worse-case should assume that will always return true. This patch adds the page_offset into the DIV_ROUND_UP for each frag. Signed-off-by: Paul Durrant Cc: Ian Campbell Cc: Wei Liu Cc: Sander Eikelenboom --- drivers/net/xen-netback/netback.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index befc413..ac35489 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -492,8 +492,18 @@ static void xenvif_rx_action(struct xenvif *vif) PAGE_SIZE); for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { unsigned int size; + unsigned int offset; + size = skb_frag_size(&skb_shinfo(skb)->frags[i]); - max_slots_needed += DIV_ROUND_UP(size, PAGE_SIZE); + offset = skb_shinfo(skb)->frags[i].page_offset; + + /* For a worse-case estimate we need to factor in + * the fragment page offset as this will affect the + * number of times xenvif_gop_frag_copy() will + * call start_new_rx_buffer(). + */ + max_slots_needed += DIV_ROUND_UP(offset + size, + PAGE_SIZE); } if (skb_is_gso(skb) && (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 || -- 1.7.10.4