netdev - Re: [PATCH] softlockup: detect bottom-half lockups

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Message-ID: <20090115140454.GH4722@google.com>
Date:	Thu, 15 Jan 2009 06:04:55 -0800
From:	Mandeep Singh Baines <msb@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, rientjes@...gle.com,
	mbligh@...gle.com, thockin@...gle.com, akpm@...ux-foundation.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] softlockup: detect bottom-half lockups

Stumbled upon ftrace tracepoints while writing this patch. Should
make life a lot easier for debugging latency issues.

bhlockup should complement ftrace. Once you've found that there's a
problem, tracing can be a big help in debugging. But assertions are
nice for finding problems you didn't know exist.

Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Mandeep Singh Baines <msb@...gle.com> wrote:
> 
> > The feature should be useful to real-time developers and developers of 
> > network and other high-performance drivers.
> 
> hm, did you know about the ftrace latency tracers:
> 
>  config IRQSOFF_TRACER
>          bool "Interrupts-off Latency Tracer"
> 
>  config PREEMPT_TRACER
>          bool "Preemption-off Latency Tracer"
> 
>  config SCHED_TRACER
>          bool "Scheduling Latency Tracer"
> 
> PREEMPT_TRACER would have shown you that softirqs-off section very nicely. 
> 
> (And if you also enable the function tracer then not just the latency 
> endpoint is shown, but also all the function calls that happened in the 
> critical section.)
> 
> 	Ingo
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