Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755206AbcCPFtN (ORCPT ); Wed, 16 Mar 2016 01:49:13 -0400 Received: from mail-pf0-f171.google.com ([209.85.192.171]:35750 "EHLO mail-pf0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752531AbcCPFtL (ORCPT ); Wed, 16 Mar 2016 01:49:11 -0400 Subject: Re: [RFC PATCH kernel] Revert "net/mlx4_core: Set UAR page size to 4KB regardless of system page size" To: Eli Cohen References: <1458037148-4475-1-git-send-email-aik@ozlabs.ru> <56E8BFFE.9000803@ozlabs.ru> <20160316051021.GC66645@x-vnc01.mtx.labs.mlnx> Cc: Or Gerlitz , Huy Nguyen , Doug Ledford , Eugenia Emantayev , Hal Rosenstock , Sean Hefty , Yishai Hadas , Linux Kernel , "linux-rdma@vger.kernel.org" , Linux Netdev List , Paul Mackerras , Carol L Soto , Yevgeny Petrilin , Brian J King From: Alexey Kardashevskiy Message-ID: <56E8F3CC.3070203@ozlabs.ru> Date: Wed, 16 Mar 2016 16:49:00 +1100 User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160316051021.GC66645@x-vnc01.mtx.labs.mlnx> Content-Type: text/plain; charset=koi8-r; 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: 1504 Lines: 42 On 03/16/2016 04:10 PM, Eli Cohen wrote: > On Wed, Mar 16, 2016 at 01:07:58PM +1100, Alexey Kardashevskiy wrote: >> >> So with v4.5 as a host, there is no actual distro available today to >> use as a guest in the next 6 months (or whatever it takes to >> backport this partucular patch back there). >> >> You could have added a module parameter to enforce the old behavoir, >> at least... >> >> And sorry but from the original commit log I could not understand >> why exactly all existing guests need to be broken. Could you please >> point me to a piece of documentation describing all this UAR >> bisuness (what is UAR, why 128 UARs are required and for what, etc). >> Thanks. >> > > We are going to send a patch that fixes this using a module parameter. > The patch will be on top of Huy's patch. > > Some background to the problem: mlx4 supported devices require 128 UAR What does UAR stand for? > pages from PCI memory space defined by BAR2-3. Each UAR page can be > any power of 2 value from 4K up to 64K. Before Huy's patch the driver > chose UAR page size to be equal to system page size. Since PowerPC's > page size is 64K this means minimum requirement of UAR pages is not > met (default UAR BAR is 8MB and only half of it is really reserved for > UARs). And what was the downside? afaict the performance was good... > More details can be found in the programmer's manual. Can you please point me to this manual on the website? I tried, honestly, could not find it. Thanks. -- Alexey