From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: [PATCH] solos-pci: Increase headroom on received packets Date: Wed, 16 Sep 2015 11:25:45 +0100 Message-ID: <1442399145.131189.56.camel@infradead.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-r8P+CyK1KM6OptLWNgiV" Cc: simon@fire.lp0.eu, guy@traverse.com.au, linux-atm-general@lists.sourceforge.net To: netdev@vger.kernel.org Return-path: Received: from casper.infradead.org ([85.118.1.10]:51259 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754803AbbIPKZt (ORCPT ); Wed, 16 Sep 2015 06:25:49 -0400 Sender: netdev-owner@vger.kernel.org List-ID: --=-r8P+CyK1KM6OptLWNgiV Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable A comment in include/linux/skbuff.h says that: * Various parts of the networking layer expect at least 32 bytes of * headroom, you should not reduce this. This was demonstrated by a panic when handling fragmented IPv6 packets: http://marc.info/?l=3Dlinux-netdev&m=3D144236093519172&w=3D2 It's not entirely clear if that comment is still valid =E2=80=94 and if it = is, perhaps netif_rx() ought to be enforcing it with a warning. But either way, it is rather stupid from a performance point of view for us to be receiving packets into a buffer which doesn't have enough room to prepend an Ethernet header =E2=80=94 it means that *every* incoming packet is going to be need to be reallocated. So let's fix that. Signed-off-by: David Woodhouse ---=20 Tested in the DMA code path; I don't believe the DMA-capable devices can still be used in MMIO mode. Simon, Guy, would you be able to test the MMIO version? diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c index 74e18b0..be8225e 100644 --- a/drivers/atm/solos-pci.c +++ b/drivers/atm/solos-pci.c @@ -805,13 +805,13 @@ static void solos_bh(unsigned long card_arg) continue; } =20 - skb =3D alloc_skb(size + 1, GFP_ATOMIC); + skb =3D alloc_skb(size + NET_SKB_PAD + 1, GFP_ATOMIC); if (!skb) { if (net_ratelimit()) dev_warn(&card->dev->dev, "Failed to allocate sk_buff for RX\n"); continue; } - + skb_reserve(skb, NET_SKB_PAD); memcpy_fromio(skb_put(skb, size), RX_BUF(card, port) + sizeof(*header), size); @@ -869,8 +869,10 @@ static void solos_bh(unsigned long card_arg) /* Allocate RX skbs for any ports which need them */ if (card->using_dma && card->atmdev[port] && !card->rx_skb[port]) { - struct sk_buff *skb =3D alloc_skb(RX_DMA_SIZE, GFP_ATOMIC); + struct sk_buff *skb =3D alloc_skb(RX_DMA_SIZE + NET_SKB_PAD, + GFP_ATOMIC); if (skb) { + skb_reserve(skb, NET_SKB_PAD); SKB_CB(skb)->dma_addr =3D dma_map_single(&card->dev->dev, skb->data, RX_DMA_SIZE, DMA_FROM_DEVICE); --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-r8P+CyK1KM6OptLWNgiV Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB MB4XDTE1MDUwNTA5NDM0MVoXDTE2MDUwNTA5NTMzNlowQjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFk ZWFkLm9yZzEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMkbm9kPbx1j/X4RVyf/pPKSYwelcco69TvnQQbKM8m8xkWjXJI1 jpJ1jMaGUZGFToINMSZi7lZawUozudWbXSKy1SikENSTJHffsdRAIlsp+hR8vWvjsKUry6sEdqPG 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