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_gonza...@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? Regards.
