Re: [Xen-devel] [RFC] Interrupt latency measurement technique

[Jonathan Fraser <jfraser@xxxxxxxxxxxx>]

I need to make the same measurements.
How did you pass the value of 'xen_timer_val' to the dom0 kernel?  I can
store it in a scratch hardware register in the SoC, but how did you do
it?

Thanks,
Jon


On Wed, 2014-08-27 at 13:07 +0300, Andrii Tseglytskyi wrote:
> 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@xxxxxxxxxxxxxxx> 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
> 
> 
> 

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