Re: Only one counter available on Pentium3

[John S. <lin...@fr...>]

William Cohen wrote:

> John Sigler wrote:
> 
>> I'm working on an "embedded" system (it's really just an x86 platform 
>> with a 128MB SSD and 256MB RAM). I've observed unusual latencies 
>> periodically on some PCI DMA operations. I thought OProfile might help 
>> to understand where the unusual latencies come from.
> 
> You might also look at the latency tracing patches like Ingo Molnar has.
> 
> http://people.redhat.com/mingo/latency-tracing-patches/

I think that patch made it into 2.6.20 (?)

The following options are set in my .config:

CONFIG_TRACE_IRQFLAGS_SUPPORT=y
# CONFIG_PRINTK_TIME is not set
# CONFIG_ENABLE_MUST_CHECK is not set
# CONFIG_MAGIC_SYSRQ is not set
# CONFIG_UNUSED_SYMBOLS is not set
# CONFIG_DEBUG_FS is not set
# CONFIG_HEADERS_CHECK is not set
# CONFIG_DEBUG_KERNEL is not set
CONFIG_LOG_BUF_SHIFT=14
CONFIG_STACKTRACE=y
CONFIG_EVENT_TRACE=y
CONFIG_FUNCTION_TRACE=y
CONFIG_WAKEUP_TIMING=y
CONFIG_LATENCY_TRACE=y
# CONFIG_CRITICAL_PREEMPT_TIMING is not set
# CONFIG_CRITICAL_IRQSOFF_TIMING is not set
CONFIG_WAKEUP_LATENCY_HIST=y
CONFIG_LATENCY_TIMING=y
CONFIG_LATENCY_HIST=y
CONFIG_MCOUNT=y
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_FRAME_POINTER=y
CONFIG_UNWIND_INFO=y
CONFIG_STACK_UNWIND=y
CONFIG_EARLY_PRINTK=y
CONFIG_X86_FIND_SMP_CONFIG=y
CONFIG_X86_MPPARSE=y
CONFIG_DOUBLEFAULT=y

But the tools are not obvious.

# ./check_dektec_input0 4140064638 0 1316 80
RATE: 38.019115 Mbit/s
PERIOD: 276913 ns
       632.311669128       386137 ns
       642.150123090       376096 ns
       642.150299889       164604 ns
       652.180122882       376978 ns
       652.180298594       165521 ns
       700.120871360       449977 ns
       700.120975781        88911 ns
       718.230122602       373120 ns
       718.230302861       170038 ns

# cat /proc/latency_trace
preemption latency trace v1.1.5 on 2.6.20.7-rt8
--------------------------------------------------------------------
  latency: 26 us, #2/2, CPU#0 | (M:rt VP:0, KP:0, SP:1 HP:1)
     -----------------
     | task: softirq-timer/0-4 (uid:0 nice:0 policy:1 rt_prio:50)
     -----------------

                  _------=> CPU#
                 / _-----=> irqs-off
                | / _----=> need-resched
                || / _---=> hardirq/softirq
                ||| / _--=> preempt-depth
                |||| /
                |||||     delay
    cmd     pid ||||| time  |   caller
       \   /    |||||   \   |   /
    <...>-4     0D..1   26us : trace_stop_sched_switched 
(__sched_text_start)


vim:ft=help

I'll give the CONFIG_PREEMPT_RT mailing list a try.

Regards.