Commit da5afbeb authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

ftrace: Optimize testing what context current is in 

The preempt_count() is not a simple location in memory, it could be part of
per_cpu code or more. Each access to preempt_count(), or one of its accessor
functions (like in_interrupt()) takes several cycles. By reading
preempt_count() once, and then doing tests to find the context against the
value return is slightly faster than using in_nmi() and in_interrupt().

Link: https://lkml.kernel.org/r/20201028115612.780796355@goodmis.org
Link: https://lkml.kernel.org/r/20201106023546.558881845@goodmis.org



Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 6e4eb9cb

include/linux/trace_recursion.h

+20 −13
Original line number Diff line number Diff line
@@ -117,22 +117,29 @@ enum { 


#define TRACE_CONTEXT_MASK	TRACE_LIST_MAX



/*

 * Used for setting context

 *  NMI     = 0

 *  IRQ     = 1

 *  SOFTIRQ = 2

 *  NORMAL  = 3

 */

enum {

	TRACE_CTX_NMI,

	TRACE_CTX_IRQ,

	TRACE_CTX_SOFTIRQ,

	TRACE_CTX_NORMAL,

};



static __always_inline int trace_get_context_bit(void)

{

	int bit;

	unsigned long pc = preempt_count();



	if (in_interrupt()) {

		if (in_nmi())

			bit = 0;



		else if (in_irq())

			bit = 1;

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

		return TRACE_CTX_NORMAL;

	else

			bit = 2;

	} else

		bit = 3;



	return bit;

		return pc & NMI_MASK ? TRACE_CTX_NMI :

			pc & HARDIRQ_MASK ? TRACE_CTX_IRQ : TRACE_CTX_SOFTIRQ;

}



static __always_inline int trace_test_and_set_recursion(int start, int max)