From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jia He Subject: Re: About pmu cycle counter usage in armv8 Date: Mon, 11 Dec 2017 14:23:54 +0800 Message-ID: References: <676baa87-777b-ca6e-41c9-7233f90740b6@gmail.com> <20171211055930.GA15672@jerin> Mime-Version: 1.0 Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" To: Jerin Jacob Return-path: Received: from mail-it0-f65.google.com (mail-it0-f65.google.com [209.85.214.65]) by dpdk.org (Postfix) with ESMTP id 356762661 for ; Mon, 11 Dec 2017 07:24:02 +0100 (CET) Received: by mail-it0-f65.google.com with SMTP id d137so13261501itc.2 for ; Sun, 10 Dec 2017 22:24:02 -0800 (PST) In-Reply-To: <20171211055930.GA15672@jerin> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi Jerin Ok And I wonder why you haven't met such problem (all rd_tsc() is 0)in your test platform? Did you use an old kernel (older than v4.5-rc1)? root@aw-host:~/linux# git describe da4e4f18afe0 v4.5-rc1-8-gda4e4f1 Maybe you need to give a warning that, the usage of High-resolution cycle counter is not correct if the kernel version is newer than v4.5-rc1-8-gda4e4f1? Cheers, Jia On 12/11/2017 1:59 PM, Jerin Jacob Wrote: > -----Original Message----- >> Date: Mon, 11 Dec 2017 13:38:25 +0800 >> From: Jia He >> To: Jerin Jacob , "dev@dpdk.org" >> >> Subject: About pmu cycle counter usage in armv8 >> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 >> Thunderbird/52.5.0 >> >> Hi Jerin >> >> In [1], I met a pmu cycle counter problem (all return value is 0) >> occasionally. >> >> And then I submited a patch to kernel maillist, but was rejected by >> maintainer at last [2]. >> >> He said: >> >> "We only intend for the in-kernel perf infrastructure to access >> >> pmccntr_el0; nothing else should touch it." > Yes. That's the reason why > 1) A warning added in documentation. > http://dpdk.org/doc/guides/prog_guide/profile_app.html > See at last > " > The PMU based scheme is useful for high accuracy performance profiling > with rte_rdtsc(). However, this method can not be used in conjunction > with Linux userspace profiling tools like perf as this scheme alters the > PMU registers state. > " > 2) By default it is disabled and not need for production systems. > Needed only for performance debugging. > >> So maybe it is not proper for dpdk to use pmu cycle counter? > But, There is no alternative in arm64 to get high resolution counter in > user space(in performance effective way) > >> [1] http://dpdk.org/ml/archives/dev/2017-November/080998.html >> >> [2]https://lkml.org/lkml/2017/11/16/22 >> >> -- >> Cheers, >> Jia >>