From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4390470F.8040503@domain.hid> Date: Fri, 02 Dec 2005 14:07:27 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Xenomai-help] i386 2.4 backport performing (too?) well References: In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigED7B517878CCCA12E51C553E" List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Klaas Gadeyne Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigED7B517878CCCA12E51C553E Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Klaas Gadeyne wrote: > With the arrival of the 2.4 i386 adeos ipipe patch for xenomai [1], I > decided to try to compile xenomai-trunk for a 2.4 kernel. This worked > flawlessly, and moreover, I got excellent latency results: >=20 > I used the "same" kernel config as for our 2.4.31 rtai3.0r5 kernel, > which is based on Takis Issaris' liveCD config. >=20 > This resulted in a maximal latency of 30 usec after a run of over 100 > minutes under heavy load (tar and dd loops, compiling, keyboard > interrupts and ping flood) [2]. >=20 > For comparison, on the same hardware platform: - the RTAI lxrt-latency > on rtai 3.0r5 (adeos oldgen r18c1 > patch for 2.4.31 also) test reports 38 usec > - the latency test of xenomai 2.01 running on a 2.6.14-ipipe-1.0-10 > kernel resulted in a latency of 80 usec. >=20 > This seems too good to be true? Can one simply compare the results of > the former RTAI lxrt-latency test with the xenomai latency test? Mmh, I tend to be sceptical as well, also remembering the results Wolfgang posted about 2.6 vs. 2.4 on low-end PPC (https://mail.gna.org/public/xenomai-core/2005-11/msg00131.html). Well, such worst-case improvement may be real if and only if there is less *kernel* code in hard-irq-off sections with 2.4. The complexity of adeos/ipipe and xenomai isn't changed between both scenarios. But I rather think that 2.4 just stresses the caches less than 2.6, thus is may be more tricky to trigger the real worst-case path. So, what we already saw with PPC: 2.4 and 2.6 may likely show similar RT performances under Xenomai, but the overall system performance is much better on low-end! However, I would be happy if this theory is too pessimistic. Jan --------------enigED7B517878CCCA12E51C553E Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFDkEcPncNeS9Q0k+IRAkaFAJ9iOnRRTV2k4GByHV2rNyO02fHoEQCg3L6c QQcq/Xs53lRseaMHb/4izIQ= =ZUC+ -----END PGP SIGNATURE----- --------------enigED7B517878CCCA12E51C553E--