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tracing: Reuse logic from perf's get_recursion_context()

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Instead of having branches that adds noise to the branch prediction, use
the addition logic to set the bit for the level of interrupt context that
the state is currently in. This copies the logic from perf's
get_recursion_context() function.

Link: https://lore.kernel.org/all/20211015161702.GF174703@worktop.programming.kicks-ass.net/

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2021-10-15 13:42:40 -04:00
parent 7ce1bb83a1
commit 9b84fadc44
2 changed files with 12 additions and 11 deletions
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11
include/linux/trace_recursion.h
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@ -137,12 +137,13 @@ enum {
static __always_inline int trace_get_context_bit(void)
{
unsigned long pc = preempt_count();
unsigned char bit = 0;
if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
return TRACE_CTX_NORMAL;
else
return pc & NMI_MASK ? TRACE_CTX_NMI :
pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ;
bit += !!(pc & (NMI_MASK));
bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));
bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
return TRACE_CTX_NORMAL - bit;
}
#ifdef CONFIG_FTRACE_RECORD_RECURSION