Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756804AbbDOUJV (ORCPT ); Wed, 15 Apr 2015 16:09:21 -0400 Received: from g4t3427.houston.hp.com ([15.201.208.55]:48704 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754385AbbDOUJG (ORCPT ); Wed, 15 Apr 2015 16:09:06 -0400 Message-ID: <552EC55B.8020907@hp.com> Date: Wed, 15 Apr 2015 13:08:59 -0700 From: Rick Jones User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Eric Dumazet CC: George Dunlap , Jonathan Davies , "xen-devel@lists.xensource.com" , Wei Liu , Ian Campbell , Stefano Stabellini , netdev , Linux Kernel Mailing List , Eric Dumazet , Paul Durrant , Christoffer Dall , Felipe Franciosi , linux-arm-kernel@lists.infradead.org, David Vrabel Subject: Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance regression on Xen References: <1428596218.25985.263.camel@edumazet-glaptop2.roam.corp.google.com> <1428932970.3834.4.camel@edumazet-glaptop2.roam.corp.google.com> <1429115934.7346.107.camel@edumazet-glaptop2.roam.corp.google.com> <552E9E8D.1080000@eu.citrix.com> <1429118948.7346.114.camel@edumazet-glaptop2.roam.corp.google.com> <552EA2BC.5000707@eu.citrix.com> <1429120373.7346.125.camel@edumazet-glaptop2.roam.corp.google.com> <552EA604.8010400@hp.com> <1429121303.7346.126.camel@edumazet-glaptop2.roam.corp.google.com> <552EABA3.30109@hp.com> <1429122734.7346.141.camel@edumazet-glaptop2.roam.corp.google.com> In-Reply-To: <1429122734.7346.141.camel@edumazet-glaptop2.roam.corp.google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1722 Lines: 36 On 04/15/2015 11:32 AM, Eric Dumazet wrote: > On Wed, 2015-04-15 at 11:19 -0700, Rick Jones wrote: > >> Well, I'm not sure that it is George and Jonathan themselves who don't >> want to change a sysctl, but the customers who would have to tweak that >> in their VMs? > > Keep in mind some VM users install custom qdisc, or even custom TCP > sysctls. That could very well be, though I confess I've not seen that happening in my little corner of the cloud. They tend to want to launch the VM and go. Some of the more advanced/sophisticated ones might tweak a few things but my (admittedly limited) experience has been they are few in number. They just expect it to work "out of the box" (to the extent one can use that phrase still). It's kind of ironic - go back to the (early) 1990s when NICs generated a completion interrupt for every individual tx completion (and incoming packet) and all everyone wanted to do was coalesce/avoid interrupts. I guess that has gone rather far. And today to fight bufferbloat TCP gets tweaked to favor quick tx completions. Call it cycles, or pendulums or whatever I guess. I wonder just how consistent tx completion timings are for a VM so a virtio_net or whatnot in the VM can pick a per-device setting to advertise to TCP? Hopefully, full NIC emulation is no longer a thing and VMs "universally" use a virtual NIC interface. At least in my little corner of the cloud, emulated NICs are gone, and good riddance. rick -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/