Messages in this thread Patch in this message | | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH 3/4] tracing: Use in_serving_softirq() to deduct softirq status. | Date | Mon, 25 Jan 2021 20:45:10 +0100 |
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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().
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/trace/trace.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 20858c3f6a046..75612d953fe04 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2589,8 +2589,7 @@ 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()) -- 2.30.0
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