Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758935AbZJPMAW (ORCPT ); Fri, 16 Oct 2009 08:00:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758801AbZJPMAV (ORCPT ); Fri, 16 Oct 2009 08:00:21 -0400 Received: from mail-px0-f171.google.com ([209.85.216.171]:54026 "EHLO mail-px0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756869AbZJPMAU (ORCPT ); Fri, 16 Oct 2009 08:00:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:reply-to:to:cc:in-reply-to:references:content-type :organization:date:message-id:mime-version:x-mailer :content-transfer-encoding; b=Kvnug8mUJfUSWq+jaZFnlXqb+EKNmIsFQ1MuEdMb9MsVD9hZCFyzwGmEoSEczNfzjP lRzVRDHVAF+2G5QoW+XZFQKkahElOdGW+xQgE9ALhK+ypo5k/nrNJKIyB8yFVvyzCx6K Z/UFelIz1Iu6KEGhudQTlAFy3j3q+lsBDo0Tc= Subject: Re: [PATCH 1/2] tracing: convert trace_clock_local() as weak function From: Wu Zhangjin Reply-To: wuzhangjin@gmail.com To: =?ISO-8859-1?Q?Am=E9rico?= Wang Cc: linux-kernel@vger.kernel.org, linux-mips , Ralf Baechle , Thomas Gleixner , Steven Rostedt , Ingo Molnar , Manuel Lauss , Atsushi Nemoto In-Reply-To: <20091016115214.GA3159@hack> References: <4205779ae74d7c4144ee6cbf4e3f15f833646356.1255692619.git.wuzhangjin@gmail.com> <20091016115214.GA3159@hack> Content-Type: text/plain; charset="UTF-8" Organization: DSLab, Lanzhou University, China Date: Fri, 16 Oct 2009 19:59:32 +0800 Message-Id: <1255694372.7084.3.camel@falcon> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2061 Lines: 51 On Fri, 2009-10-16 at 19:52 +0800, Américo Wang wrote: > 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. > Thanks, will use it in the next version. Regards, Wu Zhangjin -- 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/