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    SubjectRe: [patch 04/15] LTTng instrumentation - irq
    Mathieu Desnoyers wrote:
    > Instrumentation of IRQ related events : irq, softirq, tasklet entry and exit and
    > softirq "raise" events.
    >
    > It allows tracers to perform latency analysis on those various types of
    > interrupts and to detect interrupts with max/min/avg duration. It helps
    > detecting driver or hardware problems which cause an ISR to take ages to
    > execute. It has been shown to be the case with bogus hardware causing an mmio
    > read to take a few milliseconds.
    >
    > Those tracepoints are used by LTTng.
    >
    > About the performance impact of tracepoints (which is comparable to markers),
    > even without immediate values optimizations, tests done by Hideo Aoki on ia64
    > show no regression. His test case was using hackbench on a kernel where
    > scheduler instrumentation (about 5 events in code scheduler code) was added.
    > See the "Tracepoints" patch header for performance result detail.
    >
    > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    > CC: Thomas Gleixner <tglx@linutronix.de>
    > CC: Russell King <rmk+lkml@arm.linux.org.uk>
    > CC: Masami Hiramatsu <mhiramat@redhat.com>
    > CC: 'Peter Zijlstra' <peterz@infradead.org>
    > CC: "Frank Ch. Eigler" <fche@redhat.com>
    > CC: 'Ingo Molnar' <mingo@elte.hu>
    > CC: 'Hideo AOKI' <haoki@redhat.com>
    > CC: Takashi Nishiie <t-nishiie@np.css.fujitsu.com>
    > CC: 'Steven Rostedt' <rostedt@goodmis.org>
    > CC: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
    > ---
    > kernel/irq-trace.h | 36 ++++++++++++++++++++++++++++++++++++
    > kernel/irq/handle.c | 6 ++++++
    > kernel/softirq.c | 8 ++++++++
    > 3 files changed, 50 insertions(+)
    >
    > Index: linux-2.6-lttng/kernel/irq/handle.c
    > ===================================================================
    > --- linux-2.6-lttng.orig/kernel/irq/handle.c 2008-07-09 10:57:33.000000000 -0400
    > +++ linux-2.6-lttng/kernel/irq/handle.c 2008-07-09 10:57:35.000000000 -0400
    > @@ -15,6 +15,7 @@
    > #include <linux/random.h>
    > #include <linux/interrupt.h>
    > #include <linux/kernel_stat.h>
    > +#include "../irq-trace.h"
    >
    > #include "internals.h"
    >
    > @@ -130,6 +131,9 @@ irqreturn_t handle_IRQ_event(unsigned in
    > {
    > irqreturn_t ret, retval = IRQ_NONE;
    > unsigned int status = 0;
    > + struct pt_regs *regs = get_irq_regs();
    > +
    > + trace_irq_entry(irq, regs);
    >
    > handle_dynamic_tick(action);
    >
    > @@ -148,6 +152,8 @@ irqreturn_t handle_IRQ_event(unsigned in
    > add_interrupt_randomness(irq);
    > local_irq_disable();
    >
    > + trace_irq_exit();
    > +

    Hi Mathieu,
    What would you think tracing return value of irq handlers here?
    like:
    trace_irq_exit(retval);

    So, we can check the irq was handled correctly or not.

    Thank you,


    --
    Masami Hiramatsu

    Software Engineer
    Hitachi Computer Products (America) Inc.
    Software Solutions Division

    e-mail: mhiramat@redhat.com



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