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[1/5] asm-generic: add smp_vcond_load_relaxed()

Message ID 20241105183041.1531976-2-harisokn@amazon.com (mailing list archive)
State New
Headers show
Series [1/5] asm-generic: add smp_vcond_load_relaxed() | expand

Commit Message

Haris Okanovic Nov. 5, 2024, 6:30 p.m. UTC 
Relaxed poll until desired mask/value is observed at the specified
address or timeout.

This macro is a specialization of the generic smp_cond_load_relaxed(),
which takes a simple mask/value condition (vcond) instead of an
arbitrary expression. It allows architectures to better specialize the
implementation, e.g. to enable wfe() polling of the address on arm.

Signed-off-by: Haris Okanovic <harisokn@amazon.com>
---
 include/asm-generic/barrier.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

Comments

Christoph Lameter (Ampere) Nov. 5, 2024, 7:36 p.m. UTC | #1 
On Tue, 5 Nov 2024, Haris Okanovic wrote:

> +/**
> + * smp_vcond_load_relaxed() - (Spin) wait until an expected value at address
> + * with no ordering guarantees. Spins until `(*addr & mask) == val` or
> + * `nsecs` elapse, and returns the last observed `*addr` value.
> + *
> + * @nsecs: timeout in nanoseconds

Please use an absolute time in nsecs instead of a timeout. You do not know
what will happen to your execution thread until the local_clock_noinstr()
is run.
diff mbox series

Patch

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index d4f581c1e21d..112027eabbfc 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -256,6 +256,31 @@  do {									\
 })
 #endif
 
+/**
+ * smp_vcond_load_relaxed() - (Spin) wait until an expected value at address
+ * with no ordering guarantees. Spins until `(*addr & mask) == val` or
+ * `nsecs` elapse, and returns the last observed `*addr` value.
+ *
+ * @nsecs: timeout in nanoseconds
+ * @addr: pointer to an integer
+ * @mask: a bit mask applied to read values
+ * @val: Expected value with mask
+ */
+#ifndef smp_vcond_load_relaxed
+#define smp_vcond_load_relaxed(nsecs, addr, mask, val) ({	\
+	const u64 __start = local_clock_noinstr();		\
+	u64 __nsecs = (nsecs);					\
+	typeof(addr) __addr = (addr);				\
+	typeof(*__addr) __mask = (mask);			\
+	typeof(*__addr) __val = (val);				\
+	typeof(*__addr) __cur;					\
+	smp_cond_load_relaxed(__addr, (				\
+		(VAL & __mask) == __val ||			\
+		local_clock_noinstr() - __start > __nsecs	\
+	));							\
+})
+#endif
+
 /**
  * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
  * @ptr: pointer to the variable to wait on