From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Darbyshire-Bryant Subject: Re: OpenWRT wrong adjustment of fq_codel defaults (Was: [Codel] fq_codel_drop vs a udp flood) Date: Sat, 7 May 2016 10:57:53 +0100 Message-ID: <572DBC21.10209@darbyshire-bryant.me.uk> References: <1462125592.5535.194.camel@edumazet-glaptop3.roam.corp.google.com> <865DA393-262D-40B6-A9D3-1B978CD5F6C6@gmail.com> <1462128385.5535.200.camel@edumazet-glaptop3.roam.corp.google.com> <1462136140.5535.219.camel@edumazet-glaptop3.roam.corp.google.com> <1462201620.5535.250.camel@edumazet-glaptop3.roam.corp.google.com> <1462205669.5535.254.camel@edumazet-glaptop3.roam.corp.google.com> <1462464776.13075.18.camel@edumazet-glaptop3.roam.corp.google.com> <1462476207.13075.20.camel@edumazet-glaptop3.roam.corp.google.com> <20160506114243.4eb4f95e@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0883436651636243535==" Cc: make-wifi-fast@lists.bufferbloat.net, zajec5@gmail.com, ath10k , "codel@lists.bufferbloat.net" , "netdev@vger.kernel.org" , Jonathan Morton , Roman Yeryomin To: Jesper Dangaard Brouer , Eric Dumazet , Felix Fietkau , Dave Taht Return-path: In-Reply-To: <20160506114243.4eb4f95e@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "ath10k" Errors-To: ath10k-bounces+gldad-ath10k=m.gmane.org@lists.infradead.org List-Id: netdev.vger.kernel.org --===============0883436651636243535== Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms020109070209090704010907" --------------ms020109070209090704010907 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 06/05/16 10:42, Jesper Dangaard Brouer wrote: > Hi Felix, > > This is an important fix for OpenWRT, please read! > > OpenWRT changed the default fq_codel sch->limit from 10240 to 1024, > without also adjusting q->flows_cnt. Eric explains below that you must= > also adjust the buckets (q->flows_cnt) for this not to break. (Just > adjust it to 128) > > Problematic OpenWRT commit in question: > http://git.openwrt.org/?p=3Dopenwrt.git;a=3Dpatch;h=3D12cd6578084e > 12cd6578084e ("kernel: revert fq_codel quantum override to prevent it = from causing too much cpu load with higher speed (#21326)") I 'pull requested' this to the lede-staging tree on github. https://github.com/lede-project/staging/pull/11 One way or another Felix & co should see the change :-) > > > I also highly recommend you cherry-pick this very recent commit: > net-next: 9d18562a2278 ("fq_codel: add batch ability to fq_codel_drop(= )") > https://git.kernel.org/davem/net-next/c/9d18562a227 > > This should fix very high CPU usage in-case fq_codel goes into drop mod= e. > The problem is that drop mode was considered rare, and implementation > wise it was chosen to be more expensive (to save cycles on normal mode)= =2E > Unfortunately is it easy to trigger with an UDP flood. Drop mode is > especially expensive for smaller devices, as it scans a 4K big array, > thus 64 cache misses for small devices! > > The fix is to allow drop-mode to bulk-drop more packets when entering > drop-mode (default 64 bulk drop). That way we don't suddenly > experience a significantly higher processing cost per packet, but > instead can amortize this. I haven't done the above cherry-pick patch & backport patch creation for 4.4/4.1/3.18 yet - maybe if $dayjob permits time and no one else beats me to it :-) Kevin --------------ms020109070209090704010907 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 ZSBDbGllbnQgQ0EwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDHCYPMzi3YGrEp 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