From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-x230.google.com (mail-ig0-x230.google.com [IPv6:2607:f8b0:4001:c05::230]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 0004F21F2C3 for ; Tue, 21 Apr 2015 21:28:58 -0700 (PDT) Received: by iget9 with SMTP id t9so97617386ige.1 for ; Tue, 21 Apr 2015 21:28:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:subject:from:to:cc:date:in-reply-to:references :content-type:mime-version:content-transfer-encoding; bh=P4FUrVT+WeTEXjnlXxJDNyxsxQKiNhjwxVEvosOuJ8Q=; b=aZ8A1PL5SQdkmtuK0cUv/PEE+HpwImcRMR9kRtQe6erEfDt3cPVilhJpw+2e01d3fP MtIyN9NJ+7YidYtZ0J/GkEe2iAorZIVzg2Gea51mP+jkaGy16gCVeJcnqqRhIh70UlTZ W0+7lL9dDCRs1pnd39zTKpsNKYNiOlwmovdhNsXBGA4rJ0ylVBACZe5aGEpXBNgzcPmq au6mdSFKrx7/jLDoewm7H+LC3UbTnX/TP6r/GcJdPAsbL0TSaU10T1fIKzMNfSAcyAHB AMcUaOB98Vk4D3LhCqObxAXDcRjYm0yYvC3fR1pBXPji2c9WRpNM0uNy1MCAper/ZF6h Ajhw== X-Received: by 10.43.65.144 with SMTP id xm16mr7200088icb.57.1429676937860; Tue, 21 Apr 2015 21:28:57 -0700 (PDT) Received: from [172.19.245.82] ([172.19.245.82]) by mx.google.com with ESMTPSA id r39sm2463836ioi.2.2015.04.21.21.28.56 (version=TLSv1.2 cipher=AES128-GCM-SHA256 bits=128/128); Tue, 21 Apr 2015 21:28:56 -0700 (PDT) Message-ID: <1429676935.18561.42.camel@edumazet-glaptop2.roam.corp.google.com> From: Eric Dumazet To: "Steinar H. Gunderson" Date: Tue, 21 Apr 2015 21:28:55 -0700 In-Reply-To: <20150422040453.GB36239@sesse.net> References: <75C1DDFF-FBD2-4825-A167-92DFCF6A7713@gmail.com> <8AD4493E-EA21-496D-923D-B4257B078A1C@gmx.de> <8E4F61CA-4274-4414-B4C0-F582167D66D6@gmx.de> <2C987A4B-7459-43C1-A49C-72F600776B00@gmail.com> <14cd9e74e48.27f7.e972a4f4d859b00521b2b659602cb2f9@superduper.net> <20150422040453.GB36239@sesse.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Cc: bloat Subject: Re: [Bloat] DSLReports Speed Test has latency measurement built-in X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Apr 2015 04:29:27 -0000 On Wed, 2015-04-22 at 06:04 +0200, Steinar H. Gunderson wrote: > On Tue, Apr 21, 2015 at 08:35:21PM +1000, jb wrote: > > As I understand it (I thought) SO_SNDBUF and SO_RCVBUF are socket buffers > > for the application layer, they do not change the TCP window size either > > send or receive. > > I haven't gone into the code and checked, but from practical experience I > think you're wrong. I've certainly seen positive effects (and verified with > tcpdump) from reducing SO_SNDBUF on a server that should have no problems at > all sending data really fast to the kernel. Well, using SO_SNDBUF disables TCP autotuning. Doing so : Pros: autotuning is known to enable TCP cubic to grow cwnd to bloat levels. With small enough SO_SNDBUF, you limit this cwnd increase. Cons: Long rtt sessions might not have enough packets to utilize bandwidth. > > Then again, this kind of manual tuning trickery got obsolete for me the > moment sch_fq became available. Note that I suppose the SO_MAX_PACING rate is really helping you. Without it, TCP cubic is still allowed to 'fill the pipes' until packet losses.