From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Haigh Subject: Re: Is: SKB_MAX_LEN bites again. Was: Re: bug disabling guest interface Date: Sat, 09 Mar 2013 14:16:32 +1100 Message-ID: <513AA990.5090702@crc.id.au> References: <5139A56D.30107@crc.id.au> <00bf01ce1c34$395a4f20$ac0eed60$@jacekowski.org> <20130308203636.GA5422@phenom.dumpdata.com> <1362797836.8941.189.camel@hastur.hellion.org.uk> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============2288927404501826094==" Return-path: In-Reply-To: <1362797836.8941.189.camel@hastur.hellion.org.uk> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org This is a cryptographically signed message in MIME format. --===============2288927404501826094== Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms080201090906090805080203" This is a cryptographically signed message in MIME format. --------------ms080201090906090805080203 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable On 9/03/2013 1:57 PM, Ian Campbell wrote: >>> - change MAX_SKB_FRAGS to 19 to accommodate all guests > > Changing MAX_SKB_FRAGS is *not* an option upstream. This might be a > useful local hack but we need to drop the idea as a long term fix. I agree. Its a hack that seems to work until we have something else to=20 offer though. I'll be honest, the internals of the kernel interactions=20 like this is a bit beyond my knowledge - but I get quite a few emails of = stuff going strange. This one has increased dramatically in the past week= =2E >> Ugh. The negotiations between host and guest is probably the best >> choice. The issues you are going to hit are that you might need >> to redo the skbs to match what the frontend's max is. > > IMHO the right fix is for netback to coalesce as it copies from the > frontend if it needs to do so, it is copying anyway so it should be > cheap enough. I thought we had discussed this and someone was working o= n > implementing it. If not Annie then perhaps it was Matt or Siva (both no= w > CC'd) I did see some talk about it on the xen-devel lists quite some time ago=20 - however it seemed to die with no outcome that I could find. Maybe its=20 a good time for a nudge on the matter :) > If necessary netback could even allocate a larger order head in order t= o > accommodate very large packets, but I don't expect that to be required > to fix the immediate issue we are seeing (but gives flexibility) > > This should get us past the immediate issue of the upstream change from= > 18->16 frags thing. Longer term the negotiation will allow us to avoid= > future incompatible changes in guest and host network stacks, as well a= s > allowing frontends on other OSes (in particular Windows) to havea bette= r > chance of to DTRT. Whatever the fix, it has to be on the Dom0 kernel - as stated by others=20 in the past, it isn't a feasible fix to include changes on the client.=20 There would be too many different guest OSes that would make=20 implementation a nightmare - or in fact impossible. >> Annie, Wei, Ian - were there some RFC patches floating around >> for this? I didn't stumble across any in the list archives that I hunted for. Not=20 to say they don't exist, but I didn't find them if they do exist. --=20 Steven Haigh Email: netwiz@crc.id.au Web: https://www.crc.id.au Phone: (03) 9001 6090 - 0412 935 897 Fax: (03) 8338 0299 --------------ms080201090906090805080203 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIMdTCC BjQwggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoT DVN0YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNp Z25pbmcxKTAnBgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3 MTAyNDIxMDE1NVoXDTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1T dGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWdu aW5nMTgwNgYDVQQDEy9TdGFydENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENs 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