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SubjectRe: [PATCH] new irq tracer
On Wed, Feb 18, 2009 at 10:15:25PM +0100, Peter Zijlstra wrote:
> On Wed, 2009-02-18 at 14:53 -0500, Jason Baron wrote:
> > hi,
> >
> > Using a copule of tracepoints i've implemented an 'irq tracer' which has
> > the following column format:
> >
> > [time][irq][action][handled][cpu][length]
> >
> > for example on my system:
> >
> > [ 1038.927248381] 28 eth0 1 3 0.000002745
> > [ 1038.927544688] 28 eth0 1 3 0.000002520
> > [ 1038.927593609] 28 eth0 1 3 0.000002509
> > [ 1038.974087675] 29 ahci 1 1 0.000013135
> > [ 1038.974288475] 29 ahci 1 1 0.000005542
> > [ 1038.974414324] 29 ahci 1 1 0.000007953
> >
> > I think this patch is useful in understanding irq system behavior, and
> > for tracking down irq driver handlers that are firing too often or
> > spending too much time handling an irq. This approach could be extended
> > to the timer irq and for softirqs...
>
> The function graph tracer can already do this, it has a special section
> to recognize irq entry function, and already measures time spend.
>
> I guess with Steve's new triggers (probes or whatever they ended up
> being called) you could limit it to just IRQ entry points.
>

i did look at the graph tracer first. While it does measure irq related
functions, it does not give this level of detail concerning which irq #,
which irq handler is involved, and whether or not the irq was handled
successfully or not. So I believe this tracepoints add a level of detail
that the graph tracer does not have. Furthermore, this patch requires 2
tracepoints, not instrumentation for all kernel functions.

thanks,

-Jason





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