From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eelco Chaudron Subject: Re: [PATCH] app/testpmd: adds mlockall() to fix pages Date: Wed, 13 Sep 2017 10:55:23 +0200 Message-ID: <1a97a98b-98d1-7b0e-37b7-3976b0f2ad93@redhat.com> References: <22990026376b08418cb0eb6f028840c03e89f47f.1505221429.git.echaudro@redhat.com> <1863612.973jloI4LL@xps> <65446528.e11mYSnacx@xps> Reply-To: echaudro@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: dev@dpdk.org, jingjing.wu@intel.com, john.mcnamara@intel.com To: Thomas Monjalon , Aaron Conole Return-path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id BC8D87CFD for ; Wed, 13 Sep 2017 10:55:15 +0200 (CEST) In-Reply-To: <65446528.e11mYSnacx@xps> Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 13/09/17 00:13, Thomas Monjalon wrote: > 12/09/2017 22:29, Aaron Conole: >> Thomas Monjalon writes: >> >>> 12/09/2017 16:50, Aaron Conole: >>>> Eelco Chaudron writes: >>>> >>>>> Call the mlockall() function, to attempt to lock all of its process >>>>> memory into physical RAM, and preventing the kernel from paging any >>>>> of its memory to disk. >>>>> >>>>> When using testpmd for performance testing, depending on the code path >>>>> taken, we see a couple of page faults in a row. These faults effect >>>>> the overall drop-rate of testpmd. On Linux the mlockall() call will >>>>> prefault all the pages of testpmd (and the DPDK libraries if linked >>>>> dynamically), even without LD_BIND_NOW. >>>>> >>>>> Signed-off-by: Eelco Chaudron >>>> Acked-by: Aaron Conole >>> It is interesting, but why make it in testpmd? >>> >>> Maybe it should be documented in this guide: >>> http://dpdk.org/doc/guides/linux_gsg/nic_perf_intel_platform.html >> Well, I'm not sure what the user would be able to do to get the >> prefaulting performance without having a library they use with >> LD_PRELOAD and a function with the constructor attribute which does the >> same thing, AND export LD_BIND_NOW before linking starts. >> >> The LD_BIND_NOW simply does the symbol resolution, but there's no >> guarantee that it will fault all the code pages in to process space, and >> without an mlockall(), I'm not sure that there's any kind of guarantee >> that they don't get swapped out of resident memory (which also leads to >> later page faults). >> >> Maybe I misunderstood the question? > Maybe you misunderstood :) > > I was saying that if this improvement applies to applications, > it should be documented in the tuning guide. > I'll try to find a good place in the documentation for adding a reference to mlockall(), but will send it as a separate documentation patch. //Eelco