> -----Original Message----- > From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] > Sent: Tuesday, March 03, 2009 1:16 AM > To: Premi, Sanjeev > Cc: linux-omap@xxxxxxxxxxxxxxx > Subject: Re: omap3 cpuidle interrupt latency > > "Premi, Sanjeev" <premi@xxxxxx> writes: > > > I have noticed large interrupt latency when the cpuidle is enabled. > > e.g. response time for ping goes from avg 10-20ms to 800-1000ms. > > (I am at HEAD of the 'pm' branch) > > Is it interrupt latency in general you are measuring? or > just the interrupt latency for the smc network driver. I > think what you are seeing is the result of the SMC IRQ not > being configured as a wakeup source, thus a network interrupt > will not wake the system, but you end up waiting for the next > idle timer until the system wakes and handles the network interrupt. I used SMC as an example. The read over USB is also slow... I feel there is generic latency. Initially, I was suspecting the hrtimer functions taking long time. But that may not be the case. > > By default, I don't believe the GPIO interrupt used by the > smc is configured as a wakeup source. Have you configured > that GPIO as a wakeup source? My current measurements are based with all idle related flags 'sleep_while_idle', 'clocks_off_while_idle' and 'enable_off_mode' set at 0. Does WFI require a wakeup event? Even when system is not in 'off' stare? ~sanjeev > > Kevin > > > > The IRQs and FIQs are disabled at the beginning of the function > > omap3_enter_idle() but WFI is executed much later in > _omap_sram_idle(). > > In between, there is only one check for pending IRQs - > > omap_irq_pending() > > > > If any interrupt occurs beyond this point is it considered > by the WFI? > > > > To reduce this latency, I am planning to do either/both of thse: > > - Add more checks for pending IRQs > > - Reduce the time for which the IRQs and FIQs are disabled > > > > Benefits will depend upon the behavior of WFI. > > > > Best regards, > > Sanjeev > > > > -- > > 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 > > -- 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
