Hi Brian, On 30/11/15 21:54, Brian Norris wrote: > Hi Roger, > > On Tue, Oct 27, 2015 at 11:37:03AM +0200, Roger Quadros wrote: >> On 26/10/15 23:23, Brian Norris wrote: >>> I'm not too familiar with OMAP platforms, and I might have missed out on >>> prior discussions/context, so please forgive if I'm asking silly or old >>> questions here. >> >> No worries at all. >> >>> >>> 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. > > 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. > >> Another concern I have is that I'm not using any locking around >> gpmc_nand_irq_enable/disable(). Could this pose problems in multiple NAND >> use cases? My understanding is that it should not as the controller access >> is serialized between multiple NAND chips. > > Right, if you're touching just a NAND interrupt, and it's only used by a > single instance of this NAND controller, then the NAND controller > serialization code will handle this for you. OK. cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
