Re: [patch] Real-Time Preemption, -RT-2.6.12-rc6-V0.7.48-00

From: Ingo Molnar
Date: Tue Jun 21 2005 - 08:44:05 EST

* William Weston <weston@xxxxxxxxx> wrote:

> I also regularly see high (>200us) wakeup latencies on the Xeon/HT,
> which I don't see on the Athlon or non-HT Xeon systems. Disabling IRQ
> balancing doesn't seem to help. It's been a while since the Xeon/HT
> box has seen a non-debug kernel, but in the past, that hasn't helped
> latencies by more than a few usec.

> <idle>-0 0Dnh2 4us : find_next_bit (__schedule)
> <idle>-0 0Dnh2 4us : _raw_spin_lock (__schedule)
> <idle>-0 0Dnh3 4us!: find_next_bit (__schedule)
> <idle>-0 0Dnh3 244us : find_next_bit (__schedule)
> <idle>-0 0Dnh3 245us : _raw_spin_unlock (__schedule)

this does seem to be similar to other reports where the cause of such
latencies was some sort of hardware-level latency. (DMA related delays
or other, bus-arbitration related delays)

another possibility is that something interesting happened on another
CPU while this latency occured - to debug this please enable all-CPUs

echo 1 > /proc/sys/kernel/trace_all_cpus

and send me a new trace.

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