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Re: HVR-1600: Skipped encoder MPEG, MDL 63, 62 times - it must have dropped out of rotation



On 12-04-22 04:56 PM, Andy Walls wrote:
> 
> If, in your system, IRQ service for device A under some circumstances
> has precendence over IRQ service for the CX23418 and hence holds off its
> service; and the irq handler in the driver for device A decides to
> perform some some long I/O operations with device A; then it doesn't
> matter how fast your CPU is. 

Yes, quite true.  I was forgetting about how nasty an irq handler can be
on other hardware.

> You may wish to use perf or ftrace, or some other tool/method of
> measuring kernel interrupt handling latency to find out what causes any
> delays from the CX23418 raising its IRQ line to cx18_irq_handler() being
> called by the kernel.

Excellent idea.  I'm afraid I'm quite (read: very) green in the area of
kernel performance profiling.  But I'm smart.  Looking around, it seems
that with ftrace, I am looking for the irqsoff tracer, is that correct?
 Unfortunately my kernel doesn't have that one:

# cat /sys/kernel/debug/tracing/available_tracers
blk function_graph mmiotrace wakeup_rt wakeup function nop

I can't seem to find any useful information on using perf to analyze ISR
latency.  Any pointers?

Cheers,
b.

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