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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index a9f9c57..f6da7a0 100644 (file)
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -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

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index c5a3fbf..15d4380 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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)))) {
                /*