From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: TCP performance problems - GSO/TSO, MSS, 8139cp related Date: Fri, 11 Nov 2016 21:23:43 +0000 Message-ID: <1478899423.3892.7.camel@infradead.org> References: <20161111210500.GE1041@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-2fKvkGplDDFNEJ0FHGj8" Cc: qemu-devel@nongnu.org To: Russell King - ARM Linux , netdev@vger.kernel.org Return-path: Received: from bombadil.infradead.org ([198.137.202.9]:40870 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938551AbcKKVX4 (ORCPT ); Fri, 11 Nov 2016 16:23:56 -0500 In-Reply-To: <20161111210500.GE1041@n2100.armlinux.org.uk> Sender: netdev-owner@vger.kernel.org List-ID: --=-2fKvkGplDDFNEJ0FHGj8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2016-11-11 at 21:05 +0000, Russell King - ARM Linux wrote: >=20 > 18:59:38.782818 IP (tos 0x0, ttl 52, id 35619, offset 0, flags [DF], prot= o TCP (6), length 60) > =C2=A0=C2=A0=C2=A0 84.xx.xxx.196.61236 > 195.92.253.2.http: Flags [S], ck= sum 0x88db (correct), seq 158975430, win 29200, options [mss 1452,sackOK,TS= val 1377914597 ecr 0,nop,wscale 7], length 0 ... (MSS 1452) > 18:59:38.816371 IP (tos 0x0, ttl 64, id 25879, offset 0, flags [DF], prot= o TCP (6), length 1500) > =C2=A0=C2=A0=C2=A0 195.92.253.2.http > 84.xx.xxx.196.61236: Flags [.], se= q 1:1449, ack 154, win 235, options [nop,nop,TS val 3363137952 ecr 13779146= 27], length 1448: HTTP, length: 1448 > 18:59:38.816393 IP (tos 0x0, ttl 64, id 25880, offset 0, flags [DF], prot= o TCP (6), length 1484) > =C2=A0=C2=A0=C2=A0 195.92.253.2.http > 84.xx.xxx.196.61236: Flags [.], se= q 1449:2881, ack 154, win 235, options [nop,nop,TS val 3363137952 ecr 13779= 14627], length 1432: HTTP Can you instrument cp_start_xmit() in 8139cp.c and get it to print the value of 'mss' when this happens? All we do is take that value from skb_shinfo(skb)->gso_size, shift it a bit, and shove it in the descriptor ring. There's not much scope for a driver-specific bug. It's also *fairly* unlikely that the kernel in the guest has developed a bug and isn't setting gso_size sanely. I'm more inclined to suspect that qemu isn't properly emulating those bits. But at first glance at the code, it looks like *that's* been there for the last decade too... --=20 dwmw2 --=-2fKvkGplDDFNEJ0FHGj8 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEeAw ggXiMIIDyqADAgECAhBrp4p9CteI1lEK+Vnk57ThMA0GCSqGSIb3DQEBCwUAMH0xCzAJBgNVBAYT AklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0 aWZpY2F0ZSBTaWduaW5nMSkwJwYDVQQDEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTAeFw0xNTEyMTYwMTAwMDVaFw0zMDEyMTYwMTAwMDVaMHUxCzAJBgNVBAYTAklMMRYwFAYDVQQK Ew1TdGFydENvbSBMdGQuMSkwJwYDVQQLEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTEjMCEGA1UEAxMaU3RhcnRDb20gQ2xhc3MgMSBDbGllbnQgQ0EwggEiMA0GCSqGSIb3DQEBAQUA A4IBDwAwggEKAoIBAQC9fdr3w6J9g/Zbgv3bW1+uHht1wLUZr5gkrLtXedg17AkefMyUGwrQdvwO bhajcVmnKVxhrUwkZPXRAwZZosRHfEIi5FH7x6SV/8Sp5lZEuiMnvMFG2MzLA84J6Ws5T4NfXZ0q 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