linux-kernel - [PATCH v1 2/7] tools: Import smp_cond_load and atomic_cond

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Message-ID: <20250729022640.3134066-3-yuzhuo@google.com>
Date: Mon, 28 Jul 2025 19:26:35 -0700
From: Yuzhuo Jing <yuzhuo@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Liang Kan <kan.liang@...ux.intel.com>, Yuzhuo Jing <yzj@...ch.edu>, 
	Yuzhuo Jing <yuzhuo@...gle.com>, Andrea Parri <parri.andrea@...il.com>, 
	Palmer Dabbelt <palmer@...osinc.com>, Charlie Jenkins <charlie@...osinc.com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Kumar Kartikeya Dwivedi <memxor@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Barret Rhoden <brho@...gle.com>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, Guo Ren <guoren@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: [PATCH v1 2/7] tools: Import smp_cond_load and atomic_cond_read

Import generic barrier implementation of smp_cond_load_{acquire,relaxed}
and import macro definitions of atomic_cond_read_{acquire,relaxed}.

Signed-off-by: Yuzhuo Jing <yuzhuo@...gle.com>
---
 tools/include/asm/barrier.h  | 58 ++++++++++++++++++++++++++++++++++++
 tools/include/linux/atomic.h |  3 ++
 2 files changed, 61 insertions(+)

diff --git a/tools/include/asm/barrier.h b/tools/include/asm/barrier.h
index 0c21678ac5e6..5150c955c1c9 100644
--- a/tools/include/asm/barrier.h
+++ b/tools/include/asm/barrier.h
@@ -63,3 +63,61 @@ do {						\
 	___p1;					\
 })
 #endif
+
+#ifndef cpu_relax
+#define cpu_relax() ({})
+#endif
+
+/**
+ * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency
+ *
+ * A control dependency provides a LOAD->STORE order, the additional RMB
+ * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
+ * aka. (load)-ACQUIRE.
+ *
+ * Architectures that do not do load speculation can have this be barrier().
+ */
+#ifndef smp_acquire__after_ctrl_dep
+#define smp_acquire__after_ctrl_dep()		smp_rmb()
+#endif
+
+/**
+ * smp_cond_load_relaxed() - (Spin) wait for cond with no ordering guarantees
+ * @ptr: pointer to the variable to wait on
+ * @cond: boolean expression to wait for
+ *
+ * Equivalent to using READ_ONCE() on the condition variable.
+ *
+ * Due to C lacking lambda expressions we load the value of *ptr into a
+ * pre-named variable @VAL to be used in @cond.
+ */
+#ifndef smp_cond_load_relaxed
+#define smp_cond_load_relaxed(ptr, cond_expr) ({		\
+	typeof(ptr) __PTR = (ptr);				\
+	__unqual_scalar_typeof(*ptr) VAL;			\
+	for (;;) {						\
+		VAL = READ_ONCE(*__PTR);			\
+		if (cond_expr)					\
+			break;					\
+		cpu_relax();					\
+	}							\
+	(typeof(*ptr))VAL;					\
+})
+#endif
+
+/**
+ * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
+ * @ptr: pointer to the variable to wait on
+ * @cond: boolean expression to wait for
+ *
+ * Equivalent to using smp_load_acquire() on the condition variable but employs
+ * the control dependency of the wait to reduce the barrier on many platforms.
+ */
+#ifndef smp_cond_load_acquire
+#define smp_cond_load_acquire(ptr, cond_expr) ({		\
+	__unqual_scalar_typeof(*ptr) _val;			\
+	_val = smp_cond_load_relaxed(ptr, cond_expr);		\
+	smp_acquire__after_ctrl_dep();				\
+	(typeof(*ptr))_val;					\
+})
+#endif
diff --git a/tools/include/linux/atomic.h b/tools/include/linux/atomic.h
index 332a34177995..6baee2c41b55 100644
--- a/tools/include/linux/atomic.h
+++ b/tools/include/linux/atomic.h
@@ -36,4 +36,7 @@ void atomic_long_set(atomic_long_t *v, long i);
 #define cmpxchg_release		cmpxchg
 #endif
 
+#define atomic_cond_read_acquire(v, c) smp_cond_load_acquire(&(v)->counter, (c))
+#define atomic_cond_read_relaxed(v, c) smp_cond_load_relaxed(&(v)->counter, (c))
+
 #endif /* __TOOLS_LINUX_ATOMIC_H */
-- 
2.50.1.487.gc89ff58d15-goog