From owner-freebsd-current@FreeBSD.ORG Mon Dec 6 16:18:51 2010 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id ECA8A1065674 for ; Mon, 6 Dec 2010 16:18:50 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id C04878FC08 for ; Mon, 6 Dec 2010 16:18:50 +0000 (UTC) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 6B8F346B29; Mon, 6 Dec 2010 11:18:50 -0500 (EST) Received: from jhbbsd.localnet (smtp.hudson-trading.com [209.249.190.9]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 7D6748A009; Mon, 6 Dec 2010 11:18:49 -0500 (EST) From: John Baldwin To: freebsd-current@freebsd.org Date: Mon, 6 Dec 2010 09:44:03 -0500 User-Agent: KMail/1.13.5 (FreeBSD/7.3-CBSD-20101102; KDE/4.4.5; amd64; ; ) References: <20101205231829.GA68156@troutmask.apl.washington.edu> In-Reply-To: <20101205231829.GA68156@troutmask.apl.washington.edu> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201012060944.03196.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.6 (bigwig.baldwin.cx); Mon, 06 Dec 2010 11:18:49 -0500 (EST) X-Virus-Scanned: clamav-milter 0.96.3 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-1.9 required=4.2 tests=BAYES_00 autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on bigwig.baldwin.cx Cc: Steve Kargl Subject: Re: Process accounting/timing has broken recently X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Dec 2010 16:18:51 -0000 On Sunday, December 05, 2010 6:18:29 pm Steve Kargl wrote: > Sometime in the last 7-10 days, some one made a > change that has broken process accounting/timing. > > laptop:kargl[42] foreach i ( 0 1 2 3 4 5 6 7 8 9 ) > foreach? time ./testf > foreach? end > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 69.55 real 38.39 user 30.94 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 68.82 real 40.95 user 27.60 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 69.14 real 38.90 user 30.02 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 68.79 real 40.59 user 27.99 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 68.93 real 39.76 user 28.96 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 68.71 real 41.21 user 27.29 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 69.05 real 39.68 user 29.15 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 68.99 real 39.98 user 28.80 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 69.02 real 39.64 user 29.16 sys > Max ULP: 0.501607 for x in [-18.000000:88.709999] with dx = 1.067100e-04 > 69.38 real 37.49 user 31.67 sys > > testf is a numerically intensive program that tests the > accuracy of expf() in a tight loop. User time varies > by ~3 seconds on my lightly loaded 2 GHz core2 duo processor. > I'm fairly certain that the code does not suddenly grow/loose > 6 GFLOP of operations. The user/sys thing is a hack (and has been). We sample the PC at stathz (~128 hz) to figure out a user vs sys split and use that to divide up the total runtime (which actually is fairly accurate). All you need is for the clock ticks to fire just a bit differently between runs to get a swing in user vs system time. What I would like is to keep separate raw bintime's for user vs system time in the raw data instead, but that would involve checking the CPU ticker more often (e.g. twice for each syscall, interrupt, and trap in addition to the current once per context switch). So far folks seem to be more worried about the extra overhead rather than the loss of accuracy. -- John Baldwin