From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <50576901.2020803@xenomai.org> Date: Mon, 17 Sep 2012 20:16:33 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <5056C385.6090403@xenomai.org> <5056D4AE.2010201@web.de> <5056DA52.6040006@xenomai.org> <5056DCC5.10909@web.de> <5056E024.5020904@xenomai.org> <5056E863.4090606@siemens.com> <5056ED68.6050101@xenomai.org> <5056F09C.8050602@siemens.com> <5056F4A1.6070500@xenomai.org> <50570606.7060909@xenomai.org> <5057173C.9070108@siemens.com> <5057299B.9060804@xenomai.org> <50572B95.2060302@siemens.com> <50572D86.3040306@xenomai.org> <50573532.20700@siemens.com> <505761DF.3010609@xenomai.org> <5057666D.7080404@siemens.com> <50576725.9030601@xenomai.org> <50576804.9030109@siemens.com> <505768B9.6000704@siemens.com> In-Reply-To: <505768B9.6000704@siemens.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] IO-APIC latencies List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Xenomai On 09/17/2012 08:15 PM, Jan Kiszka wrote: > On 2012-09-17 20:12, Jan Kiszka wrote: >> On 2012-09-17 20:08, Gilles Chanteperdrix wrote: >>> On 09/17/2012 08:05 PM, Jan Kiszka wrote: >>> >>>> On 2012-09-17 19:46, Gilles Chanteperdrix wrote: >>>>> ipipe_end is a nop when called from primary domain, yes, but this is not >>>>> very different from edge irqs. Also, fasteoi become a bit like MSI: in >>>>> the same way as we can not mask MSI from primary domain, we should not >>>>> mask IO-APIC fasteoi irqs, because the cost is too prohibitive. If we >>>>> can live with MSI without masking them in primary mode, I guess we can >>>>> do the same with fasteoi irqs. >>>> >>>> MSIs are edge triggered, fasteois are still level-based. They require >>>> masking at the point you defer them - what we do and what Linux may even >>>> extend beyond that. If you mask them by raising the task priority, you >>>> have to keep it raised until Linux finally handled the IRQ. >>> >>> >>> Yes. >>> >>>> Or you >>>> decide to mask it at IO-APIC level again. >>> >>> >>> We do not want that. >>> >>>> If you keep the TPR raised, >>>> you will block more than what Linux wants to block. >>> >>> >>> The point is that if the TPR keeps raised, it means that primary domain >>> has preempted Linux, so, we want it to keep that way. Otherwise the TPR >>> gets lowered when Linux has handled the interrupt. >>> >>> A week-end of testing made me sure of one thing: it works. I assure you. >> >> Probably, in the absence of IRQF_ONESHOT Linux interrupts. No longer if >> you face threaded IRQs - I assure you. > > Well, it may work (if mask/unmask callbacks work as native) but the > benefit is gone: masking at IO-APIC level will be done again. Given that > threaded IRQs become increasingly popular, it will also be hard to avoid > them in common setups. Do they really make sense on low end platforms such as atom? We can make this new masking a compilation option. -- Gilles.