Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752886AbZKPPBt (ORCPT ); Mon, 16 Nov 2009 10:01:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752239AbZKPPBs (ORCPT ); Mon, 16 Nov 2009 10:01:48 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:49551 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752191AbZKPPBs (ORCPT ); Mon, 16 Nov 2009 10:01:48 -0500 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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1534 Lines: 36 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 -- 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/