Messages in this thread | | | Subject | Re: [PATCH] new irq tracer | From | Peter Zijlstra <> | Date | Wed, 18 Feb 2009 22:46:20 +0100 |
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On Wed, 2009-02-18 at 16:35 -0500, Jason Baron wrote: > 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.
How useful is that return value?
Much of the other data is already available, /proc/interrupts will happily tell you the source of your interrupt storm. The irq-off latency tracer will tell you if stuff takes too much time, the graph tracer can tell you what is taking how much time.
I really am having a difficult time seeing the use in such narrow tracers.
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