On 4-12-2012 11:56, Charles Steinkuehler wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 12/4/2012 4:41 AM, Michael Haberler wrote: >> A key element for an RT kernel of any kind is high-resolution >> timer support being in place in the kernel for results to make any >> sense. That can be assumed granted on PC/x86, but it cannot with >> the average ARM board. There will be _some_ timer support, but not >> necessarily a hires one. >> >> It is likely in place if somebody ported Xenomai to that board to >> start with, because that's clearly the more popular option in this >> league. And it might still mean the RT_PREEMPT kernel needs those >> patches carried over from whatever source manually. >> >> That, of course, makes the 'easier build' assumption moot, it can >> very well be harder, which raises the question why do it in the >> first place if one can have better latency with Xenomai to start >> with with less work. >> >> So much for the value of re-applying past experiences;) > It gets worse. The PREEMPT-RT code relies on SMP clean kernel code in > order to work properly. The x86 world and the Linux kernel in general > went through many pains and discovered *LOTS* of obscure bugs when > PREEMPT-RT began getting integrated into the kernel. > > That means the vendor written driver for <obscure device> on your ARM > board needs to be a clean SMP capable driver, not some hack that > relies on there never being more than one CPU in the system. And > since a *LOT* of these ARM boards only have one processor, you can > guess how often that happens. :)
Very true. When I built a PREEMPT kernel for the BeagleBone a while ago, this revealed some 'obscure' bugs in the ethernet driver / dma code. Hopefully they're fixed by now, but don't count on it! -- Bas > > - -- > Charles Steinkuehler > [email protected] > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.11 (MingW32) > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ > > iEYEARECAAYFAlC91vQACgkQLywbqEHdNFylSgCfRp/I2uvNROhYBwfVUT5mXCI9 > LhwAoNEJ3oJvsd4DVKfIx7HWvyz4kQa8 > =kJLk > -----END PGP SIGNATURE----- > > ------------------------------------------------------------------------------ > LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial > Remotely access PCs and mobile devices and provide instant support > Improve your efficiency, and focus on delivering more value-add services > Discover what IT Professionals Know. Rescue delivers > http://p.sf.net/sfu/logmein_12329d2d > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
