From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Morris Subject: Re: Detecting PREEMPT_RT Date: Sun, 20 Jan 2013 12:39:32 -0600 Message-ID: <50FC39E4.1090208@zultron.com> References: <50FB36A0.7000702@zultron.com> <50FB4BB1.7070005@osadl.org> <1819DC75-5826-4882-A2B7-20953DE3392A@mah.priv.at> <50FC2A33.5010001@osadl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Michael Haberler , linux-rt-users@vger.kernel.org To: Carsten Emde Return-path: Received: from kayako.ext.zultron.com ([67.18.89.240]:51520 "EHLO kayako.ext.zultron.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751548Ab3ATSjg (ORCPT ); Sun, 20 Jan 2013 13:39:36 -0500 In-Reply-To: <50FC2A33.5010001@osadl.org> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 01/20/2013 11:32 AM, Carsten Emde wrote: > Hi Michael, > >>> Unfortunately, this wiki article is old and unmaintained. You're probably right to be a bit suspicious when checking for the "-rt" suffix of the kernel release (uname -r). But looking for the occurrence of "PREEMPT RT" in the kernel version (uname -v) should work. An application may use the system call uname() and check the version element of the utsname structure. >> >> the utsname.version string match is fine, however: >> >>> In addition you may want to make sure the system has >>> high-resolution timers. If so, the timers in /proc/timer_list have ".resolution: 1 nsecs". An application may use the function check_timer() from cyclictest for this purpose: >>> static int check_timer(void) >>> { >>> struct timespec ts; >>> >>> if (clock_getres(CLOCK_MONOTONIC, &ts)) >>> return 1; >>> >>> return (ts.tv_sec != 0 || ts.tv_nsec != 1); >>> } >> >> Just tried this on a generic kernel (2.6.32-45-generic #102-Ubuntu SMP Wed Jan 2 21:53:06 UTC 2013 i686 GNU/Linux) and I get ts.tv_sec == 0 and ts.tv_nsec == 1, so it looks this cant be used to tell an RT_PREEMPT from a vanilla kernel > I meant boolean AND when I said "In addition". Oh, I interpreted the timer check not as a PREEMPT_RT check, but a separate check for timers, which we must confirm are available before driving heavy machinery. So, if utsname.version contains "PREEMPT RT", then load the preempt-rt module. Once the module is loaded, from an init() function, run sanity checks, including the clock_getres check above. Is that about right? Thanks for the tips, Carsten! John