From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 16 Nov 2009 16:02:09 +0100 (CET) Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:49566 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by ftp.linux-mips.org with ESMTP id S1493394AbZKPPCC (ORCPT ); Mon, 16 Nov 2009 16:02:02 +0100 Received: from [192.168.23.10] (really [74.67.89.75]) by hrndva-omta01.mail.rr.com with ESMTP id <20091116150154011.VNOJ4007@hrndva-omta01.mail.rr.com>; Mon, 16 Nov 2009 15:01:54 +0000 Subject: Re: [PATCH v8 01/16] tracing: convert trace_clock_local() as weak function From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Wu Zhangjin Cc: Ralf Baechle , Frederic Weisbecker , Ingo Molnar , Nicholas Mc Guire , David Daney , Richard Sandiford , Patrik Kluba , Thomas Gleixner , Michal Simek , "Maciej W . Rozycki" , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, zhangfx@lemote.com, zhouqg@gmail.com In-Reply-To: <9dc81a7a9e5a292cccdf465c533a2b08d19d6021.1258177321.git.wuzhangjin@gmail.com> References: <9dc81a7a9e5a292cccdf465c533a2b08d19d6021.1258177321.git.wuzhangjin@gmail.com> Content-Type: text/plain Organization: Kihon Technologies Inc. Date: Mon, 16 Nov 2009 10:01:52 -0500 Message-Id: <1258383712.22249.452.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 Content-Transfer-Encoding: 7bit Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 24914 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: rostedt@goodmis.org Precedence: bulk X-list: linux-mips On Sat, 2009-11-14 at 14:33 +0800, Wu Zhangjin wrote: > From: Wu Zhangjin > > trace_clock_local() is based on the arch-specific sched_clock(), in X86, > it is tsc(64bit) based, which can give very high precision(about 1ns > with 1GHz). but in MIPS, the sched_clock() is jiffies based, which can > give only 10ms precison with 1000 HZ. which is not enough for tracing, > especially for Real Time system. > > so, we need to implement a MIPS specific sched_clock() to get higher > precision. There is a tsc like clock counter register in MIPS, whose > frequency is half of the processor, so, if the cpu frequency is 800MHz, > the time precision reaches 2.5ns, which is very good for tracing, even > for Real Time system. > > but 'Cause it is only 32bit long, which will rollover quickly, so, such > a sched_clock() will bring with extra load, which is not good for the > whole system. so, we only need to implement a arch-specific > trace_clock_local() for tracing. as a preparation, we convert it as a > weak function. > > The MIPS specific trace_clock_local() is coming in the next two patches. > > Acked-by: Frederic Weisbecker > Signed-off-by: Wu Zhangjin Acked-by: Steven Rostedt -- Steve