From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 09 Nov 2009 03:10:25 +0100 (CET) Received: from mail-ew0-f216.google.com ([209.85.219.216]:61364 "EHLO mail-ew0-f216.google.com" rhost-flags-OK-OK-OK-OK) by ftp.linux-mips.org with ESMTP id S1493478AbZKICKS (ORCPT ); Mon, 9 Nov 2009 03:10:18 +0100 Received: by ewy12 with SMTP id 12so2853651ewy.0 for ; Sun, 08 Nov 2009 18:10:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:received:date:from:to:cc :subject:message-id:references:mime-version:content-type :content-disposition:in-reply-to:user-agent; bh=+WrPRlO4P9cpE3gY3O6uBwhwLeIyBGAQLXj6m/J5WyA=; b=do4QebKyVs7Iouj+MJIioHPMXrYbJYPKPzMHCTfitb8h8XsOJFPWb45iRiA5AFJIi1 VU8XBxxlllSqx167QzQcrgS9zcgqNo82IxvQbQjPqWSvMXZDIyNWvsQbypMv1nv3IplS lPIfo11XBZDRxWxfTT/PATdKgBW1EGYviCnXc= 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=qxrPxYA9r99mUwTrKJAkijIUFB+NcxqW8ADhfuwAcRBxktPuizBRB+I7TiagPL9MYQ wv7C2xo6XBmWm3i0q2fa77tzy7B0gnntplgcwQkE3JcyqGFMTFiHhjNZFjx7neivOJFz 2YqPVXmxs1qQHpjY5vMw6eAz0eoXX6QfZGLZk= Received: by 10.216.88.202 with SMTP id a52mr2362570wef.101.1257732611281; Sun, 08 Nov 2009 18:10:11 -0800 (PST) Received: from nowhere (ADijon-552-1-106-222.w90-33.abo.wanadoo.fr [90.33.185.222]) by mx.google.com with ESMTPS id 10sm4966144eyd.8.2009.11.08.18.10.07 (version=SSLv3 cipher=RC4-MD5); Sun, 08 Nov 2009 18:10:08 -0800 (PST) Received: by nowhere (nbSMTP-1.00) for uid 1000 (using TLSv1/SSLv3 with cipher RC4-MD5 (128/128 bits)) fweisbec@gmail.com; Mon, 9 Nov 2009 03:10:14 +0100 (CET) Date: Mon, 9 Nov 2009 03:10:12 +0100 From: Frederic Weisbecker To: Wu Zhangjin Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, Thomas Gleixner , Ralf Baechle , Richard Sandiford , Nicholas Mc Guire , David Daney , Adam Nemet , Patrik Kluba Subject: Re: [PATCH -v6 01/13] tracing: convert trace_clock_local() as weak function Message-ID: <20091109021009.GB13153@nowhere> References: <747deea2f18d5ccffe842df95a9dd1c86251a958.1256569489.git.wuzhangjin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <747deea2f18d5ccffe842df95a9dd1c86251a958.1256569489.git.wuzhangjin@gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) 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: 24757 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: fweisbec@gmail.com Precedence: bulk X-list: linux-mips On Mon, Oct 26, 2009 at 11:13:18PM +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 two patches. > > Signed-off-by: Wu Zhangjin Yep, if trace_clock_local() had to be a strict alias to sched_clock(), we would have simply used sched_clock(). If an arch need to implement it another way, then yeah making it weak is a good thing. Acked-by: Frederic Weisbecker