Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758430AbZJPL71 (ORCPT ); Fri, 16 Oct 2009 07:59:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753571AbZJPL71 (ORCPT ); Fri, 16 Oct 2009 07:59:27 -0400 Received: from mail-pw0-f42.google.com ([209.85.160.42]:40780 "EHLO mail-pw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756483AbZJPL70 (ORCPT ); Fri, 16 Oct 2009 07:59:26 -0400 X-Greylist: delayed 384 seconds by postgrey-1.27 at vger.kernel.org; Fri, 16 Oct 2009 07:59:26 EDT DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=wYAQ38mZ1wLmu/bqqZsx5DUSFw9waVKwdgbt1hsy/tebUWr2Ga+2p5PbR973XGjs63 zavOQYqtA13l6wgzPekNQ648tPF/OZQqyCjTDjZadxI8xOZec5suAQCGzACMrzUcf6db Jz8xykb3nGaOiOazf7eMPJpXI8jsg09hygCC0= Date: Fri, 16 Oct 2009 19:52:14 +0800 From: =?utf-8?Q?Am=C3=A9rico?= Wang To: Wu Zhangjin Cc: linux-kernel@vger.kernel.org, linux-mips , Ralf Baechle , Thomas Gleixner , Steven Rostedt , Ingo Molnar , Manuel Lauss , Atsushi Nemoto Subject: Re: [PATCH 1/2] tracing: convert trace_clock_local() as weak function Message-ID: <20091016115214.GA3159@hack> References: <4205779ae74d7c4144ee6cbf4e3f15f833646356.1255692619.git.wuzhangjin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4205779ae74d7c4144ee6cbf4e3f15f833646356.1255692619.git.wuzhangjin@gmail.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2216 Lines: 60 On Fri, Oct 16, 2009 at 07:38:24PM +0800, Wu Zhangjin wrote: >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 patch. > >Signed-off-by: Wu Zhangjin >--- > kernel/trace/trace_clock.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > >diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c >index 20c5f92..a04dc18 100644 >--- a/kernel/trace/trace_clock.c >+++ b/kernel/trace/trace_clock.c >@@ -26,7 +26,7 @@ > * Useful for tracing that does not cross to other CPUs nor > * does it go through idle events. > */ >-u64 notrace trace_clock_local(void) >+u64 __attribute__((weak)) notrace trace_clock_local(void) We have __weak. > { > unsigned long flags; > u64 clock; >-- >1.6.2.1 > >-- >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/ -- Live like a child, think like the god. -- 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/