From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4CD67B77.2000502@domain.hid> Date: Sun, 07 Nov 2010 11:12:07 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4CC82C8D.3080808@domain.hid> <4CD1E890.5010702@domain.hid> <4CD1EC2F.4040603@domain.hid> <4CD1ED16.8030103@domain.hid> <4CD1EDA8.10007@domain.hid> <4CD1F33C.5070208@domain.hid> <4CD1F3F5.5080505@domain.hid> <4CD1F4FE.9020908@domain.hid> <4CD1F69B.9070100@domain.hid> <4CD1F906.1070703@domain.hid> <4CD1FABD.1080301@domain.hid> <4CD2612C.2070507@domain.hid> <4CD279F7.7070502@domain.hid> <4CD27C46.8010302@domain.hid> <4CD27DC2.7060607@domain.hid> <4CD2A96B.3080001@domain.hid> <4CD2B2A7.9010900@domain.hid> <4CD2C50F.1090604@domain.hid> <4CD32E76.3080004@domain.hid> <4CD33F0C.1050403@domain.hid> <4CD340AA.60002@domain.hid> <4CD34355.5020304@domain.hid> <4CD35DC7.1000507@domain.hid> <4CD3DAC5.6000400@domain.hid> <4CD4A0EF.1@domain.hid> <4CD5B9FC.6050602@domain.hid> <4CD5BC82.6060106@domain.hid> <1289083796.1842.239.camel@domain.hid> <4CD5FA26.4090504@domain.hid> <4CD663F2.2080704@domain.hid> <1289124227.1842.283.camel@domain.hid shift> <4CD67A92.5090009@domain.hid> In-Reply-To: <4CD67A92.5090009@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] Potential problem with rt_eepro100 List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: "xenomai@xenomai.org" Jan Kiszka wrote: > Am 07.11.2010 11:03, Philippe Gerum wrote: >> On Sun, 2010-11-07 at 09:31 +0100, Gilles Chanteperdrix wrote: >>> Jan Kiszka wrote: >>>>>> Anyway, after some thoughts, I think we are going to try and make the >>>>>> current situation work instead of going back to the old way. >>>>>> >>>>>> You can find the patch which attempts to do so here: >>>>>> http://sisyphus.hd.free.fr/~gilles/sched_status.txt >>>>> Ack. At last, this addresses the real issues without asking for >>>>> regression funkiness: fix the lack of barrier before testing XNSCHED in >>>> Check the kernel, we actually need it on both sides. Wherever the final >>>> barriers will be, we should leave a comment behind why they are there. >>>> Could be picked up from kernel/smp.c. >>> We have it on both sides: the non-local flags are modified while holding >>> the nklock. Unlocking the nklock implies a barrier. >> I think we may have an issue with this kind of construct: >> >> xnlock_get_irq*(&nklock) >> xnpod_resume/suspend/whatever_thread() >> xnlock_get_irq*(&nklock) >> ... >> xnlock_put_irq*(&nklock) >> xnpod_schedule() >> xnlock_get_irq*(&nklock) >> send_ipi >> =====> xnpod_schedule_handler on dest CPU >> xnlock_put_irq*(&nklock) >> xnlock_put_irq*(&nklock) >> >> The issue would be triggered by the use of recursive locking. In that >> case, the source CPU would only sync its cache when the lock is actually >> dropped by the outer xnlock_put_irq* call and the inner >> xnlock_get/put_irq* would not act as barriers, so the remote >> rescheduling handler won't always see the XNSCHED update done remotely, >> and may lead to a no-op. So we need a barrier before sending the IPI in >> __xnpod_test_resched(). > > That's what I said. > > And we need it on the reader side as an rmb(). This one we have, in xnpod_schedule_handler. -- Gilles.