From owner-freebsd-chat@FreeBSD.ORG Sun Apr 23 19:12:17 2006 Return-Path: X-Original-To: freebsd-chat@freebsd.org Delivered-To: freebsd-chat@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CB43516A40F for ; Sun, 23 Apr 2006 19:12:17 +0000 (UTC) (envelope-from dugger@hotlz.com) Received: from www.hotlz.com (freedom.hotlz.com [209.20.218.52]) by mx1.FreeBSD.org (Postfix) with ESMTP id 48E9143D55 for ; Sun, 23 Apr 2006 19:12:17 +0000 (GMT) (envelope-from dugger@hotlz.com) Received: from [172.27.240.45] (henry.local.hotlz.com [172.27.240.45]) by www.hotlz.com (8.13.3/8.13.3) with ESMTP id k3NJCFvu045889 for ; Sun, 23 Apr 2006 12:12:15 -0700 (PDT) (envelope-from dugger@hotlz.com) Message-ID: <444BD18F.9080302@hotlz.com> Date: Sun, 23 Apr 2006 12:12:15 -0700 From: Don Dugger User-Agent: Mozilla Thunderbird 1.0.7 (Macintosh/20050923) X-Accept-Language: en-us, en MIME-Version: 1.0 To: freebsd-chat@freebsd.org References: <200604231525.k3NFP64X003155@mist.nodomain> In-Reply-To: <200604231525.k3NFP64X003155@mist.nodomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: Why is not more FreeBSD software written in C++? X-BeenThere: freebsd-chat@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Non technical items related to the community List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 23 Apr 2006 19:12:17 -0000 As I sit here on this beautiful day. It dawns on me that tried improving a program a few years back by changing printf("%s",s) to puts(s) and the puts() make it run much slower. I never found out why. I also remember doing research a year or so ago on GC and the guy that are proponents have some interesting ideas on performance. http://www.iecc.com/gclist/GC-faq.html Now I'm getting out of here its to nice of day... Don 8) Dan Strick wrote: >On Sunday 23 Apr 2006 02:03, Benjamin Lutz wrote: > > >>On Saturday 22 April 2006 17:11, Dan Strick wrote: >> >> >>>On Thursday 20 Apr 2006 22:58, Benjamin Lutz wrote: (this line corrected) >>> >>> >>>>The example above is not exactly a realworld example. Even if you stick >>>>to plain C, a repeated putchar(' ') is 1-2 orders of magnitude slower >>>>than aggregating those characters and write()'ing them every few dozen >>>>chars. >>>> >>>> >>>This might seem obvious, but is it really true? I wrote a program that >>>tries it both ways with the output redirected to /dev/null and discovered >>>that filling a 24 character buffer and doing a write() takes about 11 times >>>as much cpu time as 24 putchar()s. Perhaps a buffer larger than a "few >>>dozen chars" would be useful. There must be a moral here somewhere. :-) >>> >>> >>Yes, it is really true. Since I don't know what your test is, I've created >>my own. >> >>... >> >>All files are compiled with gcc/g++ and the -O2 option. I'm running them on >>a Mac Mini under Linux. >> >>And the results are (I've run that command several times and picked a line >>that shows an average run time): >> >>$ time ./test_putchar > /dev/null >>./test_putchar > /dev/null 0.39s user 0.00s system 97% cpu 0.397 total >>$ time ./test_write > /dev/null >>./test_write > /dev/null 0.02s user 0.01s system 82% cpu 0.029 total >>$ time ./test_iostream > /dev/null >>./test_iostream > /dev/null 0.94s user 0.00s system 99% cpu 0.950 total >>$ time ./test_string > /dev/null >>./test_string > /dev/null 0.21s user 0.00s system 97% cpu 0.213 total >> >> >>That quite clearly shows that my prediction that using putchar is "1-2 orders >>of magnitude slower" is accurate. It also shows the points you and others >>have made that iostream is slower than C's I/O mechanisms. >> >>If we take the two most sensible variants, test_write and test_iostream, and >>have them write into a file, we get these numbers: >> >>$ time ./test_write > foo >>./test_write > foo 0.01s user 0.16s system 95% cpu 0.180 total >>$ time ./test_string > foo >>./test_string > foo 0.20s user 0.02s system 98% cpu 0.223 total >> >>Which is a small enough difference to be irrelevant. The large I/O performance >>advantage of the write(2) variant over the C++ string variant vanishes as >>soon as the code actually does something remotely useful. >> >> >> > >In order to make sure that we are comparing apples to apples and not >to oranges, I copied Benjamin Lutz's test programs and ran them on my >machine, a 2.8 GHz Intel P4 running FreeBSD 5.4. The repetition counts >in the programs were increased from 50K to 500K and the programs were >compiled with the -O2 option using whatever version of GNU gcc/g++ comes >standard with FreeBSD 5.4. > >times for output to /dev/null: > >test_putchar: 0.140u 0.000s 0:00.14 100.0% 5+180k 0+0io 0pf+0w >test_write: 0.163u 0.413s 0:00.57 100.0% 5+171k 0+0io 0pf+0w >test_iostream: 3.673u 0.015s 0:03.69 99.7% 5+179k 0+0io 0pf+0w >test_string: 0.789u 0.007s 0:00.79 98.7% 5+188k 0+0io 0pf+0w > >times for output to file foo: > >test_putchar: 0.145u 0.040s 0:01.82 9.8% 5+194k 0+232io 0pf+0w >test_write: 0.133u 1.333s 0:01.84 79.3% 6+170k 0+232io 0pf+0w >test_iostream: 3.635u 0.077s 0:03.73 99.1% 6+197k 0+232io 0pf+0w >test_string: 0.772u 0.076s 0:01.84 45.6% 8+213k 0+232io 0pf+0w > >My results show something quite different. Even though the buffer >size used by Benjamin's write() test (61 bytes) is much larger than >the one I used (only 24 bytes), the write() test to /dev/null still >takes about 4 times longer than the putchar() test. As one might >expect, the write() test spends most of its time in the kernel doing >all those write() system calls. The putchar() test (i.e. stdio) >is probably using a 1K byte buffer. > >I cannot explain Benjamin's results on a Mac Mini running Linux. >His write() test to /dev/null took almost no system time. Note that >on his system the write() test to a real file consumed 16 times as >much system time as the write() test to /dev/null (best guess since >the precision of his time measurement was so limited). On my system >the ratio was about 3 to one. His I/O system must be radically >different from mine. Does anyone know why? What does Linux do >differently than FreeBSD? > >I stand by my suggestion that using putchar() might not be slower. >On my system it was much faster. > >I also note that while most of the tests writing to a real file used >about the same real time, there were really huge differences in cpu >time. Test_putchar was the big winner, running 4.5 times faster than >test_string, 8 times faster than test_write, and 20 times faster than >test_iostream. Such differences in cpu consumption can be important >even when the processes are i/o bound because other processes running >on the same system may be cpu bound. > >Dan Strick >_______________________________________________ >freebsd-chat@freebsd.org mailing list >http://lists.freebsd.org/mailman/listinfo/freebsd-chat >To unsubscribe, send any mail to "freebsd-chat-unsubscribe@freebsd.org" > >