From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <454B15C5.1050803@domain.hid> Date: Fri, 03 Nov 2006 11:11:17 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Fwd: Re: [Xenomai-help] invalid use of FPU in Xenomai context] References: <4548C170.1000504@domain.hid> <4548F8BE.90809@domain.hid> <454901B6.80606@domain.hid> <454B0FA0.9080307@domain.hid> <454B1363.8080805@domain.hid> In-Reply-To: <454B1363.8080805@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig2B796B337688B246C738F4C2" Sender: jan.kiszka@domain.hid List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: Xenomai help This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig2B796B337688B246C738F4C2 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Jeff Webb wrote: >> >>> Jan Kiszka wrote: >>> >>>> Jeff Webb wrote: >>>> >>>>> Does anyone else have an AMD system that can verify my results? >>>> >>>> I have an old Athlon 800. Maybe we are lucky and it exposes the prob= lem >>>> when the kernel is optimised for it. I'm going to give this a try, b= ut >>>> it may take a few days (and a free time slot). >>> >>> Thank you. I appreciate you giving it a try when you get some free >>> time. I was able to work around the problem by writing the queue dat= a >>> in smaller chunks (or use an i686 kernel), so I am not in urgent need= of >>> an immediate fix. I do think it's important to fix this bug eventual= ly, >>> so I didn't want it to slip through the cracks. >>> >>> >>>>> The problem seems to be connected with the size of writes to Xenoma= i >>>>> pipes. This example uses POSIX message queues, but I had a similar= >>>>> problem a while back with RTAI pipes. Maybe this tells us the prob= lem >>>>> is in the nucleus pipe code? Just a guess. The problem seems to >>>>> affect >>>>> both 2.4 and 2.6 systems, and goes back to at least Xenomai 2.2.1. >>>> >>>> Maybe, maybe not. Pipes remain fairly unrelated to FPU usage, so the= re >>>> is still /at least/ one piece missing in the puzzle. >>> >>> True. It is very strange that the amount of data in the write call e= nds >>> up affecting the FPU context. >> >> >> I found the reason: "3-dimensional" memcpy (__memcpy3d/_mmx_memcpy) >> >> http://lxr.free-electrons.com/source/include/asm-i386/string.h#285 >> >> It's an optimised memcpy for 3DNow CPUs that is used with blocks >=3D = 512 >> bytes. It messes up with the FPU state and may get trapped by other >> issues as well (blind access to "current" in order to test >> in_interrupt()). I don't have an answer for this right now beyond "don= 't >> switch on AMD optimisations when using Xenomai". But that's a bit >> unsatisfying. >> >> Another way would be to wrap any memcpy access from Xenomai context, b= ut >> that's likely impractical (think of all the drivers). >=20 > I see other ways to solve this issue: > - either we disable the use of the mmx memcpy in string.h if > ipipe_current_domain is not root This is what came to my mind as well meanwhile. > - or we allow the exception to happen for threads in primary mode with > the XNFPU bit set and call xnarch_restore_fpu in xnpod_fault_handler in= > this case. Given that this is a special case for a subset of x86[_64] CPUs, I rather think we should go for the first variant. Should be simpler. Jan --------------enig2B796B337688B246C738F4C2 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFSxXFniDOoMHTA+kRAg1TAJ9uMc3BVg2rNZkrWVuZUfP54NSliQCbBAcw t7zXiXUz5e98FravFAFhdyE= =syO0 -----END PGP SIGNATURE----- --------------enig2B796B337688B246C738F4C2--