On Fri, 2013-04-05 at 19:21 +0000, Seiji Aguchi wrote:
> [Issue]
>
> Currently, irq vector handlers for tracing are just
> copied non-trace handlers by simply inserting tracepoints.
>
> It is difficult to manage the codes.
>
> [Solution]
This as a separate patch actually makes things more confusing to review.
It should be merged into the previous patch. If you want to break up the
changes, I would first add the entering_irq(), and exiting_irq() as
patch 1, and then do the rest of the changes in patch 2.
-- Steve
> This patch shares common codes between non-trace and trace handlers
> as follows to make them manageable and readable.
>
> Non-trace irq handler:
> smp_irq_handler()
> {
> entering_irq(); /* pre-processing of this handler */
> __smp_irq_handler(); /*
> * common logic between non-trace and trace handlers
> * in a vector.
> */
> exiting_irq(); /* post-processing of this handler */
>
> }
>
> Trace irq_handler:
> smp_trace_irq_handler()
> {
> entering_irq(); /* pre-processing of this handler */
> trace_irq_entry(); /* tracepoint for irq entry */
> __smp_irq_handler(); /*
> * common logic between non-trace and trace handlers
> * in a vector.
> */
> trace_irq_exit(); /* tracepoint for irq exit */
> exiting_irq(); /* post-processing of this handler */
>
> }
>
> If tracepoints can place outside entering_irq()/exiting_irq() as follows, it
> looks \
> cleaner.
>
> smp_trace_irq_handler()
> {
> trace_irq_entry();
> smp_irq_handler();
> trace_irq_exit();
> }
>
> But it doesn't work.
> The problem is with irq_enter/exit() being called. They must be called before
> \
> trace_irq_enter/exit(), because of the rcu_irq_enter() must be called before
> any \
> tracepoints are used, as tracepoints use rcu to synchronize.
>
> As a possible alternative, we may be able to call irq_enter() first as
> follows if \
> irq_enter() can nest.
>
> smp_trace_irq_hander()
> {
> irq_entry();
> trace_irq_entry();
> smp_irq_handler();
> trace_irq_exit();
> irq_exit();
> }
>
> But it doesn't work, either.
> If irq_enter() is nested, it may have a time penalty because it has to check
> if it \
> was already called or not. The time penalty is not desired in performance
> sensitive \
> paths even if it is tiny.
>
> Signed-off-by: Seiji Aguchi <seiji.agu...@hds.com>
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