Messages in this thread | | | Subject | Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback | From | Marc Zyngier <> | Date | Mon, 7 Aug 2017 13:56:20 +0100 |
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On 28/07/17 15:06, Marc Gonzalez wrote: > On 27/07/2017 20:17, Florian Fainelli wrote: > >> On 07/26/2017 12:13 PM, Måns Rullgård wrote: >> >>> Florian Fainelli writes: >>> >>>> On 07/25/2017 06:29 AM, Måns Rullgård wrote: >>>> >>>>> Marc Gonzalez <marc_gonzalez@sigmadesigns.com> writes: >>>>> >>>>>> On 25/07/2017 15:16, Måns Rullgård wrote: >>>>>> >>>>>>> What happened to the patch adding the proper combined function? >>>>>> >>>>>> It appears you're not CCed on v2. >>>>>> >>>>>> https://patchwork.kernel.org/patch/9859799/ >>>>>> >>>>>> Doug wrote: >>>>>>> Yes, you understand correctly. The irq_mask_ack method is entirely >>>>>>> optional and I assume that is why this issue went undetected for so >>>>>>> long; however, it is slightly more efficient to combine the functions >>>>>>> (even if the ack is unnecessary) which is why I chose to do so for my >>>>>>> changes to the irqchip-brcmstb-l2 driver where I first discovered this >>>>>>> issue. How much value the improved efficiency has is certainly >>>>>>> debatable, but interrupt handling is one area where people might care >>>>>>> about such a small difference. As the irqchip-tango driver maintainer >>>>>>> you are welcome to decide whether or not the irq_mask_ack method makes >>>>>>> sense to you. >>>>>> >>>>>> My preference goes to leaving the irq_mask_ack callback undefined, >>>>>> and let the irqchip framework use irq_mask and irq_ack instead. >>>>> >>>>> Why would you prefer the less efficient way? >>>>> >>>> >>>> Same question here, that does not really make sense to me. >>>> >>>> The whole point of this patch series is to have a set of efficient and >>>> bugfree (or nearly) helper functions that drivers can rely on, are you >>>> saying that somehow using irq_mask_and_ack is exposing a bug in the >>>> tango irqchip driver and using the separate functions does not expose >>>> this bug? >>> >>> There is currently a bug in that the function used doesn't do what its >>> name implies which can't be good. Using the separate mask and ack >>> functions obviously works, but combining them saves a lock/unlock >>> sequence. The correct combined function has already been written, so I >>> see no reason not to use it. >> >> Marc/Mason, are you intending to get this patch accepted in order to >> provide a quick bugfix targeting earlier kernels with the tango irqchip >> driver or is this how you think the correct fix for the tango irqchip >> driver is as opposed to using Doug's fix? > > Hello Florian, > > I am extremely grateful for you and Doug bringing the defect to > my attention, as it was indeed causing an issue which I had not > found the time to investigate. > > The reason I proposed an alternate patch is that > 1) Doug didn't seem to mind, 2) simpler code leads to fewer bugs > and less maintenance IME, and 3) I didn't see many drivers using > the irq_mask_ack() callback (9 out of 86) with a few misusing it, > by defining irq_mask = irq_mask_ack. > > As you point out, my patch might be slightly easier to backport > than Doug's (TBH, I hadn't considered that aspect until you > mentioned it). > > Has anyone ever quantified the performance improvement of > mask_ack over mask + ack?
Aren't you the one who is in position of measuring this effect on the actual HW that uses this?
Thanks,
M. -- Jazz is not dead. It just smells funny...
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