From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <44CD099F.9010507@domain.hid> Date: Sun, 30 Jul 2006 21:33:51 +0200 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Xenomai-help] Beginner's question / testsuite / latency References: <442248c90607201417m24729b7cs23a8b82b719ff1cc@domain.hid> <200607221152.34298.bidsonux@domain.hid> <44C25DB0.50601@domain.hid> <200607282317.34990.bidsonux@domain.hid> <44CB6EB3.5070707@domain.hid> <1154282619.4970.25.camel@domain.hid> In-Reply-To: <1154282619.4970.25.camel@domain.hid> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig9AF4061CEA831EC74F5EAC06" 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: rpm@xenomai.org Cc: xenomai@xenomai.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig9AF4061CEA831EC74F5EAC06 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable Philippe Gerum wrote: > On Sat, 2006-07-29 at 16:20 +0200, Jan Kiszka wrote: >>>> :|func 6 xnintr_clock_handler (__ipipe_dispatch_wired) >>>> :|func 6 xnintr_irq_handler (xnintr_clock_handler) >>>> :|func 7 xnpod_announce_tick (xnintr_irq_handler) >>>> :|func 8+ xntimer_do_tick_aperiodic (xnpod_announce_tick) >>>> :|func 9 xnthread_periodic_handler (xntimer_do_tick_aperiod= ic) >>>> :|func 10 xnpod_resume_thread (xnthread_periodic_handler) >>>> :|[21559] 11+ xnpod_resume_thread (xnthread_periodic_handler) >>>> :|func 13+ xnthread_periodic_handler (xntimer_do_tick_aperiod= ic) >> ... >> >>>> :|func 363+ xnthread_periodic_handler (xntimer_do_tick_aperiod= ic) >> That are a lot of overruns. Haven't counted, but it should be one >> xnthread_periodic_handler per missed 100 us period (20000 / 100 =3D 20= 0!). >> [BTW, I think we should handle even this failure scenario without >> looping. >=20 > We need to loop in the aperiodic handler in order to catch timers that > could have elapsed while processing the current tick. However, No, that was not what I meant. I know that we need the timer loop. But I was thinking of something like this for the tick handler's error path: if (unlikely((timer.date +=3D timer.interval) < now)) timer.date =3D now + timer.interval - (now - timer.date) % timer.interval; > xnpod_wait_thread_period() - over which rt_task_wait_period() is based = - > does not loop, but rather computes the actual count of overruns by > substracting the current time from the deadline. =2E..but by looping for some scenarios instead of dividing for all. Why optimising the slow path here? >=20 > Which brings us an interesting question: why does the aperiodic handler= > loop frenetically in the first place? I would be pretty interested in > checking the TSC values returned by xnarch_get_cpu_tsc() while spinning= > inside this deadly loop... You can already read those TSCs: each trace point got recorded with the current TSC value, fresh from the hardware. I rather think, also when looking at Julien's second trace, that we have some issue with X in user-space here, probably in combination with weird VIA hardware stalling IRQ delivery for a "few" microseconds. Let's see if the irqbench gives similar results. Jan --------------enig9AF4061CEA831EC74F5EAC06 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 iD8DBQFEzQmfniDOoMHTA+kRAl/HAJ9ElhaJpVL3+XrRJyKHEmMS18IKeQCfZEbe FwQ8JzbdcEHOMs80tBZlKxo= =cm6D -----END PGP SIGNATURE----- --------------enig9AF4061CEA831EC74F5EAC06--