From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <45D2CF9E.40308@domain.hid> Date: Wed, 14 Feb 2007 10:00:14 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Xenomai-help] CONFIG_PREEMPT & irqbench References: <45D25145.3000407@domain.hid> <45D2CE27.5040303@domain.hid> In-Reply-To: <45D2CE27.5040303@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig1531B78334531466DF9BA4C2" 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: Markus.Franke@domain.hid Cc: Xenomai-help@domain.hid This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig1531B78334531466DF9BA4C2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Jan Kiszka wrote: > Markus Franke wrote: >> Dear all, >> >> I am running some latency tests with irqbench/irqloop. I am wondering >> whether it would be possible to achieve better results when activating= >> CONFIG_PREEMPT and CONFIG_PREEMPT_VOLUNTARILY during the kernel >> configuration and running irqloop in User Mode over this kernel? >=20 > Nope. >=20 >> Does it make any sense? >=20 > Nope. :) >=20 >> I think in theory it should give better results because >> this irqloop runs in secondary(linux) domain when started, right? An >> increasing preemptibility of the linux kernel should be better for the= >> irqloop-task. >=20 > The Linux kernel is already fully preemptible by Xenomai once you > applied the I-pipe patch. Therefore, you are free to pick the Linux > preemption strategy according to your *Linux* load, independent of what= > the real-time part needs. >=20 > Unless you have interactive Linux programs running, I can suggest to > pick PREEMPT_VOLUNTARILY or even PREEMPT_NONE, specifically on low-end > hardware. >=20 >> All tests were made under heavy I/O and CPU load by means of "dd", >> "pingflood" and "cpuburn". Nevertheless, I can only achieve worse >> results when activating CONFIG_PREEMPT. >=20 > Do you have CONFIG_DEBUG_PREEMPT set as well then? This option still as= > a small but measurable impact on Xenomai due to micro-dependencies that= > as scheduled to be removed in the near future. Hmm, I should have better said "tiny". This experience is based on I-pipe tracer observations, and I guess you don't have that thing on, have you? How much is the difference? How long did you measure to exclude noise. Jan --------------enig1531B78334531466DF9BA4C2 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFF0s+eniDOoMHTA+kRAh3EAJ9rkLU1T78cgmny5vZ3pT/HGLqo4wCffqN7 aNta0jdlNLnwHxgOyoPLHy8= =5Boy -----END PGP SIGNATURE----- --------------enig1531B78334531466DF9BA4C2--