RE: [PATCH v9 3/3] trace,x86: code-sharing between non-trace and trace irq handlers

From: H. Peter Anvin
Date: Sat Feb 16 2013 - 00:42:06 EST

Fair enough. Sounds good.

Seiji Aguchi <seiji.aguchi@xxxxxxx> wrote:

>> > How important is it that the tracepoint is *inside* the enter/exit
>> > handling? If not, it would be simpler to just do:
>> >
>> > smp_trace_irq_handler()
>> > {
>> > trace_irq_entry();
>> > smp_irq_handler();
>> > trace_irq_exit();
>> > }
>> >
>> > ... which seems a bit cleaner. If this isn't possible, then this
>> > patch is fine, but please add to the patch description why the
>> > wrapper isn't doable.
>> 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.
>I tried to place tracepoints outside the enter/exit handling. But it
>didn't work because of the rcu_irq_enter().
>> Now perhaps we could do this and have trace_irq_entry().
>> Not only that, the tracepoint callbacks expect irq_enter() to already
>be called.
>> Hmm, if irq_enter() can nest, which I think it can, perhaps we can
>> irq_enter() first. I'm not sure if that will screw up the second
>> irq_entry() inside smp_irq_handler().
>> smp_trace_irq_hander()
>> {
>> irq_entry();
>> trace_irq_entry();
>> smp_irq_handler();
>> trace_irq_exit();
>> irq_exit();
>> }
>If irq_enter() is nested, it may have a time penalty because it has to
>check if it was already called or not.
>It doesn't satisfy a goal of this patch.
>Therefore, I think current coding is reasonable.
>I will update the patch description.

Sent from my mobile phone. Please excuse brevity and lack of formatting.
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