Messages in this thread | | | Date | Fri, 9 May 2003 10:23:31 +0200 | From | mikpe@csd ... | Subject | Re: how to measure scheduler latency on powerpc? realfeel doesn't work due to /dev/rtc issues |
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William Lee Irwin III writes: > On Thu, 8 May 2003, William Lee Irwin III wrote: > >>>>> Why would you want to use an interrupt? Just count jiffies in sched.c > > On Thu, May 08, 2003 at 11:52:29PM -0400, Chris Friesen wrote: > > I'm trying to get a feel for the maximum time from an interrupt coming in > > until the userspace handler gets notified. On intel you can program the > > hardware to generate interupts through /dev/rtc. The powerpc doesn't seem > > to support this. > > Jiffies are not accurate enough, I am expecting max latencies in the 1-2 ms > > range. > > Unfortunately no. USB/Firewire/Ethernet on the desktop, ethernet/serial > > for compactPCI. > > I want to find an additional programmable interrupt source. It bites that > > cheap PCs have this, and the powerpc doesn't. > > Try the timebase instead.
On all Moto PPCs I've checked, the time-base runs at 1/4 the bus clock rather than at the core clock like we're used to on x86.
I believe many PPCs allow you to program one of the performance counters to count core clocks. Be advised though that many Moto PPCs in the 750-7410 range have an errata that prevents using performance counter interrupts, so you'd have to run the counter in non-interrupting mode.
This isn't available to user-space (yet), so you'd also have to hack the kernel to use this facility. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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