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tracing: Use in_serving_softirq() to deduct softirq status.

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PREEMPT_RT does not report "serving softirq" because the tracing core
looks at the preemption counter while PREEMPT_RT does not update it
while processing softirqs in order to remain preemptible. The
information is stored somewhere else.
The in_serving_softirq() macro and the SOFTIRQ_OFFSET define are still
working but not on the preempt-counter.

Use in_serving_softirq() macro which works on PREEMPT_RT. On !PREEMPT_RT
the compiler (gcc-10 / clang-11) is smart enough to optimize the
in_serving_softirq() related read of the preemption counter away.
The only difference I noticed by using in_serving_softirq() on
!PREEMPT_RT is that gcc-10 implemented tracing_gen_ctx_flags() as
reading FLAG, jmp _tracing_gen_ctx_flags(). Without in_serving_softirq()
it inlined _tracing_gen_ctx_flags() into tracing_gen_ctx_flags().

Link: https://lkml.kernel.org/r/20210125194511.3924915-4-bigeasy@linutronix.de

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Sebastian Andrzej Siewior 2021-01-25 20:45:10 +01:00 committed by Steven Rostedt (VMware)
parent 0c02006e6f
commit fe427886bf
1 changed files with 1 additions and 2 deletions
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3
kernel/trace/trace.c
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@ -2590,8 +2590,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
trace_flags |= TRACE_FLAG_NMI;
if (pc & HARDIRQ_MASK)
trace_flags |= TRACE_FLAG_HARDIRQ;
if (pc & SOFTIRQ_OFFSET)
if (in_serving_softirq())
trace_flags |= TRACE_FLAG_SOFTIRQ;
if (tif_need_resched())