From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: I/O operations priority in RTOS Date: Sun, 05 Jun 2011 11:44:53 +0200 Message-ID: <4DEB5015.7070601@web.de> References: <4DEA1BA9.7020303@unican.es> <4DEA1F22.6000603@unican.es> <20110604234214.GA30640@opentech.at> <4DEB427F.9020104@steinhoff.de> <20110605092854.GA7576@opentech.at> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig69FFE98731176D4A21E4AC5A" Cc: Armin Steinhoff , Monica Puig-Pey , linux-rt-users@vger.kernel.org To: Nicholas Mc Guire Return-path: Received: from fmmailgate03.web.de ([217.72.192.234]:45529 "EHLO fmmailgate03.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754734Ab1FEJoz (ORCPT ); Sun, 5 Jun 2011 05:44:55 -0400 In-Reply-To: <20110605092854.GA7576@opentech.at> Sender: linux-rt-users-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig69FFE98731176D4A21E4AC5A Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2011-06-05 11:28, Nicholas Mc Guire wrote: > On Sun, 05 Jun 2011, Armin Steinhoff wrote: >=20 >> Nicholas Mc Guire wrote: >>> On Sat, 04 Jun 2011, Monica Puig-Pey wrote: >>> >>>> Hello, >>>> I'm studying how to develop drivers in a real time OS and how do the= y >>>> work. I'm using Ubuntu 10.04 with the 2.6.31-11-rt patch installed.= >>>> I would like to know the priority when executing open(), read(), wri= te() >>>> and close() operations. >>>> In my example the thread which is using the driver runs with 10 RTPR= IO, >>>> but I don't know what happens in kernel context with the priority wh= en >>>> running the I/O operations. >>>> Thank you for your help, I don't know where to learn about this. >>>> >>> [] >>> Also when using bottom half mechanisms you need to take into account = the >>> priority of the kernel thread that manages the defered work items, so= >>> rt-drivers may have a different structure than normal drivers. >> >> That's the reason why I prefer UIO based user space drivers ! >> > ...and how to resolve DMA ? if DMA were resolved cleanly I would agree.= Regarding that limitation, there is some hope: "next-generation" UIO is called VFIO. Useful for exclusively assigning virtual PCI functions of network adapters etc. to user space stacks or hypervisors like QEMU/KVM (for device pass-through). But it's not mainline yet. And it obviously requires an IOMMU. But the key point remains: "exclusively". Anything else cannot be modeled efficiently via UIO or VFIO. Jan --------------enig69FFE98731176D4A21E4AC5A Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.15 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/ iEYEARECAAYFAk3rUBUACgkQitSsb3rl5xTz7QCfYRptp4jvCpds8qFUQCPPSsxy EMwAnRYrgyWbBgOO2Kf6YO9eA5RuziwN =F1nK -----END PGP SIGNATURE----- --------------enig69FFE98731176D4A21E4AC5A--