On 02/23/2017 08:17 AM, Henning Schild wrote: > On Thu, 23 Feb 2017 06:00:15 -0800 > Dan Zach <[email protected]> wrote: > >> Dear forum, >> >> On the Jetson TK1 inmate I use linux 4.8.2 with PREEMPT-RT patch. >> I measure a 1KHz high priority task based on hrtimer events that >> measures it's own jitter. Run jailhouse cell stats for your RT-cell and watch the MMIO traps. I guess it will heavily trap on RT. RT heavily accesses the GICD that needs to be emulated in hardware >> >> The worst case, I get 400uS jitter on 1mS tick - not so bad, but the Uh, okay? With the root cell idling? CONFIG_HZ_1000?
Uhm -- What's your clocksource? Could you please post /proc/timer_list? >> interesting thing is that the jitter stays as low as 50uS, untill I >> start activity on the root cell, especially GUI. >> >> So the questions is: if the non-root cell is completely isolated from >> the root: separate physical memory, PPI from its local timer, where >> this cross influence can come from? > > Well the cells are not completely isolated, some shared resources > remain. The jitter you are seeing is caused by those, i.e. caches and > busses. And GPU workloads would likely stress exactly those. Yep, mainly shared system bus and caches. Others like MMIO dispatching and IRQ reinjection cause (at least measurable) latencies. I already did some measurements to get worst case latencies, but I never hit anything like that, interestingly. Do those latencies also occur if you use an Preempt-RT patched kernel without Jailhouse when the GPU gets stressed? Ralf > > Henning > >> Thanks >> Dan >> > -- You received this message because you are subscribed to the Google Groups "Jailhouse" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
