Re: omap3 cpuidle interrupt latency

[Kevin Hilman <khilman@deeprootsystems.com>]

"Premi, Sanjeev" <premi@ti.com> 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.

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?

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
>
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