Re: [RFC] Interrupt latency measurement technique

[Andrii Tseglytskyi <andrii.tseglytskyi@globallogic.com>]

Test setup is the following:

Platform - Jacinto6 (OMAP5) with two ARMv7 cores (Cortex A15), 1.5 Gb of RAM
Hypervisor - Xen 4.4 stable
Dom0 - Linux 3.8 running with 2 vcpus, 128 Mb RAM
DomU was not launched during the test

Regards,
Andrii


On Wed, Aug 27, 2014 at 12:14 PM, Andrii Tseglytskyi
<andrii.tseglytskyi@globallogic.com> wrote:
> Hi,
>
> I need to measure IRQ latency introduced by Xen: (GIC -> Xen IRQ
> handler -> Dom0 IRQ handler)
> I need to know how many time I spend in Xen IRQ handler.
>
> Can someone comment - is the following algorithm works:
>
> - in function xen/arch/arm/gic.c: gic_interrupt() store timer counter value:
> xen_timer_val = READ_SYSREG64(CNTPCT_EL0) - READ_SYSREG64(CNTVOFF_EL2)
>
> - in any IRQ handler in dom0 store timer counter value:
> dom0_timer_val = READ_SYSREG64(CNTPCT_EL0)
>
> - calculate time diff in nanoseconds:
> time_diff_ns = ticks_to_ns(dom0_timer_val - xen_timer_val)
>
> Using this technique I measured display IRQ latency and got about
> - 20 to 30 usec latency on 1 GHz MPU frequency
> - 10 to 20 usec latencyon 1.5 GHz MPU frequency
>
> Are these numbers expectable? Can this technique be used?
>
> Regards,
> Andrii
>
> --
>
> Andrii Tseglytskyi | Embedded Dev
> GlobalLogic
> www.globallogic.com



-- 

Andrii Tseglytskyi | Embedded Dev
GlobalLogic
www.globallogic.com