Commit 9b84fadc authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

tracing: Reuse logic from perf's get_recursion_context() 

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: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 7ce1bb83

include/linux/trace_recursion.h

+6 −5
Original line number Diff line number Diff line
@@ -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

kernel/trace/ring_buffer.c

+6 −6
Original line number Diff line number Diff line
@@ -3168,13 +3168,13 @@ trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer) 
{

	unsigned int val = cpu_buffer->current_context;

	unsigned long pc = preempt_count();

	int bit;

	int bit = 0;



	if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))

		bit = RB_CTX_NORMAL;

	else

		bit = pc & NMI_MASK ? RB_CTX_NMI :

			pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;

	bit += !!(pc & (NMI_MASK));

	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK));

	bit += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));



	bit = RB_CTX_NORMAL - bit;



	if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {

		/*