From owner-svn-src-head@FreeBSD.ORG Mon May 11 01:30:32 2009 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 1CB4B106564A; Mon, 11 May 2009 01:30:32 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from mail04.syd.optusnet.com.au (mail04.syd.optusnet.com.au [211.29.132.185]) by mx1.freebsd.org (Postfix) with ESMTP id A93668FC08; Mon, 11 May 2009 01:30:31 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from c122-106-172-38.carlnfd1.nsw.optusnet.com.au (c122-106-172-38.carlnfd1.nsw.optusnet.com.au [122.106.172.38]) by mail04.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id n4B1UR6C004570 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 11 May 2009 11:30:28 +1000 Date: Mon, 11 May 2009 11:30:26 +1000 (EST) From: Bruce Evans X-X-Sender: bde@delplex.bde.org To: Chagin Dmitry In-Reply-To: <20090509204559.GA4626@dchagin.static.corbina.ru> Message-ID: <20090511102521.W12504@delplex.bde.org> References: <200905071424.n47EOos1058369@svn.freebsd.org> <20090508111302.C1275@besplex.bde.org> <20090509204559.GA4626@dchagin.static.corbina.ru> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Bruce Evans Subject: Re: svn commit: r191883 - head/sys/compat/linux X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 May 2009 01:30:32 -0000 On Sun, 10 May 2009, Chagin Dmitry wrote: > On Fri, May 08, 2009 at 11:45:16AM +1000, Bruce Evans wrote: >> On Thu, 7 May 2009, Dmitry Chagin wrote: >> >>> Log: >>> Linux exports HZ value to user space via AT_CLKTCK auxiliary vector entry, >>> which is available for Glibc as sysconf(_SC_CLK_TCK). If AT_CLKTCK entry is >>> not exported, Glibc uses 100. >> >> This cannot work for older applications/glibc's that have CLK_TCK hard-coded. > > yes, I know. Glibc versions prior to 2.2.1 uses hardcoded CLK_TCK value. >>> - >>> -#define CONVTCK(r) (r.tv_sec * CLK_TCK + r.tv_usec / (1000000 / CLK_TCK)) >>> +#define CONVTCK(r) (r.tv_sec * hz + r.tv_usec / (1000000 / hz)) >> >> hz has very little to do with statistics clock ticks. The frequency of the >> statistics clock in FreeBSD is given by stathz. stathz will normally only >> equal hz if the statistics clock is the same as the scheduling clock. >> stathz is a bogus value too since the clock most relevant for them is the >> cputicker and the statistics clock is only used to divide them up. >> > > Thank you! > >> Anyway, this patch is backwards. The bug was that the value exported to >> user space didn't match the value here. The value cannot be changed in > > hmm, r189362. hz exported to user space via AT_CLKTCK. Bug in r189362. Now larger. CLK_TCK = 100 should be exported to user space via AT_CLKTCK. >> either FreeBSD or Linux without breaking compatibility. It is even >> harder to change in emulators than in a full O/S distribution since the >> full distribution can more reasonably drop support for all old >> applications. A correct emulator would have to have an array of values >> for each "constant" sysconf() value with the arrays index by the O/S >> version and maybe the libc version being emulated :-(. > > I will try to make the hard-coded CLK_TCK support. It will depend > on value of compat.linux.osrelease (2.2 I guess). Er, it should be constant (= old CLK_TCK = 100). Old applications are unlikely to look at compat.linx.osrelease and change their behaviour depending on it, and anyway they cannot know what to do with an osrelease newer than themself. New applications won't care if AT_CLKTCK returns the old value of CLK_TCK, unless the value is increased significantly (say to 1 million) to give more accuracy. Linux itself does this, at least in 2.6.10: % ./arch/ia64/ia32/binfmt_elf32.c: % #undef CLOCKS_PER_SEC % #define CLOCKS_PER_SEC IA32_CLOCKS_PER_SEC % #define IA32_CLOCKS_PER_SEC 100 /* Cast in stone for IA32 Linux */ This ia32 value is used for Linux own emulation of compat32. It has to be cast in stone since previous mistakes cast it there. So does the native ia32 value, but that is not so well commented. The Linux native ia64 value might be variable because it doesn't have any mistakes to be compatible with. % ./fs/binfmt_elf.c: % NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC); This maps AT_CLKTCK to CLOCKS_PER_SEC. Related mistakes are responsible for mapping CLK_TCK to CLOCKS_PER_SEC. IIRC, POSIX.1-1988 narrowly escaped the bug of specifying CLK_TCK to be the same as CLOCKS_PER_SEC, It still has the bug of specifying CLK_TCK at all. This is partly fixed in POSIX.1-1990 by specifying CLK_TCK as obsolescent and saying that CLK_TCK may be #defined as (the variable) sysconf(_SC_CLK_TCK), and is fixed in POSIX.1-2001 by removing CLK_TCK. % ./include/asm-x86_64/param.h: % #ifdef __KERNEL__ % # define HZ 1000 /* Internal kernel timer frequency */ % # define USER_HZ 100 /* .. some user interfaces are in "ticks */ % #define CLOCKS_PER_SEC (USER_HZ) /* like times() */ % #endif Most arches distinguish between the kernel clock(s) and values returned to userland using HZ/USER_HZ like this, so that the latter can be kept constant. Apparently native x86_64 is too old to have not inherited the mistake. % ./include/asm-i386/param.h: % #ifdef __KERNEL__ % # define HZ 1000 /* Internal kernel timer frequency */ % # define USER_HZ 100 /* .. some user interfaces are in "ticks" */ % # define CLOCKS_PER_SEC (USER_HZ) /* like times() */ % #endif The mistake is oldest in i386. % ./include/asm-ia64/param.h: % #ifdef __KERNEL__ % # include /* mustn't include outside of #ifdef __KERNEL__ */ % # ifdef CONFIG_IA64_HP_SIM % /* % * Yeah, simulating stuff is slow, so let us catch some breath between % * timer interrupts... % */ % # define HZ 32 % # else % # define HZ 1024 % # endif % # define USER_HZ HZ % # define CLOCKS_PER_SEC HZ /* frequency at which times() counts */ % #else % /* % * Technically, this is wrong, but some old apps still refer to it. The proper way to % * get the HZ value is via sysconf(_SC_CLK_TCK). % */ % # define HZ 1024 % #endif ia64 (itanium?) is the main arch for which USER_HZ is the same as HZ. The only(?) others are m68knommu, alpha and h8300. According the the comment, broken apps have related problems for HZ. If linux-later-than-2.6.10 has fixed this, then it would have to have a new syscall for times() and for any other interface that uses "clock ticks" (mainly clock()), and the FreeBSD emulator would have to emulate these. Linux apparently doesn't have new interfaces, so emulators cannot have them and cannot fix the mistakes without making a larger mess. Bruce