From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Fri, 15 Oct 2021 13:42:40 -0400
Subject: tracing: Reuse logic from perf's get_recursion_context()
Git-commit: 9b84fadc444de5456ab5f5487e2108311c724c3f
Patch-mainline: v5.16-rc1
References: git-fixes
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>
Acked-by: Petr Pavlu <petr.pavlu@suse.com>
---
include/linux/trace_recursion.h | 11 ++++++-----
kernel/trace/ring_buffer.c | 12 ++++++------
2 files changed, 12 insertions(+), 11 deletions(-)
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index a9f9c5714e65..f6da7a03bff0 100644
--- 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 c5a3fbf19617..15d4380006e3 100644
--- 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)))) {
/*