From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-he1eur01on0058.outbound.protection.outlook.com ([104.47.0.58] helo=EUR01-HE1-obe.outbound.protection.outlook.com) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1axaFj-0007ZS-Hk for ath10k@lists.infradead.org; Tue, 03 May 2016 13:20:40 +0000 Subject: Re: [Codel] fq_codel_drop vs a udp flood References: <1462125592.5535.194.camel@edumazet-glaptop3.roam.corp.google.com> <865DA393-262D-40B6-A9D3-1B978CD5F6C6@gmail.com> From: Kevin Darbyshire-Bryant Message-ID: <5728A589.6010107@darbyshire-bryant.me.uk> Date: Tue, 3 May 2016 14:20:09 +0100 MIME-Version: 1.0 In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============3512072735359589560==" Sender: "ath10k" Errors-To: ath10k-bounces+kvalo=adurom.com@lists.infradead.org To: ath10k@lists.infradead.org --===============3512072735359589560== Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms050707070801010005080205" --------------ms050707070801010005080205 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 03/05/16 03:26, Dave Taht wrote: > On Sun, May 1, 2016 at 11:20 AM, Jonathan Morton wrote: >>> On 1 May, 2016, at 20:59, Eric Dumazet wrote= : >>> >>> fq_codel_drop() could drop _all_ packets of the fat flow, instead of = a >>> single one. >> Unfortunately, that could have bad consequences if the =E2=80=9Cfat fl= ow=E2=80=9D happens to be a TCP in slow-start on a long-RTT path. Such a= flow is responsive, but on an order-magnitude longer timescale than may = have been configured as optimum. >> >> The real problem is that fq_codel_drop() performs the same (excessive)= amount of work to cope with a single unresponsive flow as it would for a= true DDoS. Optimising the search function is sufficient. > Don't think so. > > I did some tests today, (not the fq_codel batch drop patch yet) > > > As for cake struggling to cope: > > root@apu2:/home/d/git/tc-adv/tc# ./tc -s qdisc show dev enp2s0 > > qdisc cake 8018: root refcnt 9 bandwidth 100Mbit diffserv4 flows rtt 10= 0.0ms raw > Sent 219736818 bytes 157121 pkt (dropped 989289, overlimits 1152272 re= queues 0) > backlog 449646b 319p requeues 0 > memory used: 2658432b of 5000000b > capacity estimate: 100Mbit > Bulk Best Effort Video Voice > thresh 100Mbit 93750Kbit 75Mbit 25Mbit > target 5.0ms 5.0ms 5.0ms 5.0ms > interval 100.0ms 100.0ms 100.0ms 100.0ms > pk_delay 0us 5.2ms 92us 48us > av_delay 0us 5.1ms 4us 2us > sp_delay 0us 5.0ms 4us 2us > pkts 0 1146649 31 49 > bytes 0 1607004053 2258 8779 > way_inds 0 0 0 0 > way_miss 0 15 2 1 > way_cols 0 0 0 0 > drops 0 989289 0 0 > marks 0 0 0 0 > sp_flows 0 0 0 0 > bk_flows 0 1 0 0 > last_len 0 1514 66 138 > max_len 0 1514 110 487 I think it's interesting that the memory used is only a little of 55% of the autoconfigured max buffer size, so cake_enqueue won't have gone into its 'buffer full' cake_drop routine - I do wonder if should it ever get there that it should 'use a shovel' of 64 packets rather than teaspoon of iterating dropping single packets. The above also suggests that cake is spending time dropping packets over the target threshold individually. Does/could cake codel drop do something like 'drop sufficient bytes (in packet lumps) to get that flow back under target threshold- after ECN signalling' in one go, up to some packet number limit (64)? Again the idea is to really jump on the naughty flow! > > ... > > But I am very puzzled as to why flow isolation would fail in the face > of this overload. > >> - Jonathan Morton >> > > --------------ms050707070801010005080205 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC DYEwggY0MIIEHKADAgECAgEeMA0GCSqGSIb3DQEBBQUAMH0xCzAJBgNVBAYTAklMMRYwFAYD VQQKEw1TdGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0 ZSBTaWduaW5nMSkwJwYDVQQDEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTAe Fw0wNzEwMjQyMTAxNTVaFw0xNzEwMjQyMTAxNTVaMIGMMQswCQYDVQQGEwJJTDEWMBQGA1UE ChMNU3RhcnRDb20gTHRkLjErMCkGA1UECxMiU2VjdXJlIERpZ2l0YWwgQ2VydGlmaWNhdGUg U2lnbmluZzE4MDYGA1UEAxMvU3RhcnRDb20gQ2xhc3MgMSBQcmltYXJ5IEludGVybWVkaWF0 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