Brian, On 02/12/15 08:56, Brian Norris wrote: > Hi Roger, > > On Tue, Dec 01, 2015 at 04:41:16PM +0200, Roger Quadros wrote: >> On 30/11/15 21:54, Brian Norris wrote: >>> On Tue, Oct 27, 2015 at 11:37:03AM +0200, Roger Quadros wrote: >>>> On 26/10/15 23:23, Brian Norris wrote: >>>>> On Fri, Sep 18, 2015 at 05:53:22PM +0300, Roger Quadros wrote: >>>>>> - Remove NAND IRQ handling from omap-gpmc driver, share the GPMC IRQ >>>>>> with the omap2-nand driver and handle NAND IRQ events in the NAND driver. >>>>>> This causes performance increase when using prefetch-irq mode. >>>>>> 30% increase in read, 17% increase in write in prefetch-irq mode. >>>>> >>>>> Have you pinpointed the exact causes for the performance increase, or >>>>> can you give an educated guess? AIUI, you're reducing the number of >>>>> interrupts needed for NAND prefetch mode, but you're also removing a bit >>>>> of abstraction and implementing hooks that look awfully like the >>>>> existing abstractions: >>>>> >>>>> + int (*nand_irq_enable)(enum gpmc_nand_irq irq); >>>>> + int (*nand_irq_disable)(enum gpmc_nand_irq irq); >>>>> + void (*nand_irq_clear)(enum gpmc_nand_irq irq); >>>>> + u32 (*nand_irq_status)(void); >>>>> >>>>> That's not really a problem if there's a good reason for them (brcmnand >>>>> implements similar hooks because of quirks in the implementation of >>>>> interrupts across various BRCM SoCs, and it's not worth writing irqchip >>>>> drivers for those cases). I'm mainly curious for an explanation. >>>> >>>> I have both implementations with me. My guess is that the 20% performance >>>> gain is due to absence of irqchip/irqdomain translation code. >>>> I haven't investigated further though. >>> >>> I don't have much context for whether this makes sense or not. According >>> to your tests, you're getting ~800K interrupts over ~15 seconds. So >>> should you start noticing performance hits due to abstraction at 53K >>> interrupts per second? >> >> Yes, this was my understanding. > > Am I computing wrong, or is that a pretty insane rate of interrupts?
I don't have the test board with me right now and so can't tell you for sure if the mtd tests took 15 seconds or more. I can try it out on a different board that I have and let you know for sure about how many interrupts we get per second. > >>> But anyway, I'm not sure that completely answered my question. My >>> question was whether you were removing the irqchip code solely for >>> performance reasons, or are there others? >> >> Yes. Only for performance reasons. > > Hmm, that's not my favorite answer. I'd prefer that more analysis was > done here before scrapping irqchip... I agree. We could retain the irqchip model till we have more satisfying analysis. > > But maybe that's not too bad. It seems like your patch set overall is a > net positive for disentangling some of arch/ and drivers/. :) > > I'll take another pass over your patch set, but if things are looking > better, how do you expect to merge this? There are significant portions > that touch at least 2 or 3 different subsystem trees, AFAICT. Tony could create an immutable branch with all the dts and memory changes. You could base the mtd changes on top of that? cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
