The following commit has been merged into the perf/core branch of tip:
Commit-ID: 96450ead16527cbef559b5bd046182e731228f95
Gitweb: https://git.kernel.org/tip/96450ead16527cbef559b5bd046182e731228f95
Author: Suren Baghdasaryan <surenb@xxxxxxxxxx>
AuthorDate: Fri, 22 Nov 2024 09:44:14 -08:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 02 Dec 2024 12:01:37 +01:00
seqlock: add raw_seqcount_try_begin
Add raw_seqcount_try_begin() to opens a read critical section of the given
seqcount_t if the counter is even. This enables eliding the critical
section entirely if the counter is odd, instead of doing the speculation
knowing it will fail.
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20241122174416.1367052-1-surenb@xxxxxxxxxx
---
include/linux/seqlock.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 5298765..22c2c48 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -319,6 +319,28 @@ SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex)
})
/**
+ * raw_seqcount_try_begin() - begin a seqcount_t read critical section
+ * w/o lockdep and w/o counter stabilization
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ *
+ * Similar to raw_seqcount_begin(), except it enables eliding the critical
+ * section entirely if odd, instead of doing the speculation knowing it will
+ * fail.
+ *
+ * Useful when counter stabilization is more or less equivalent to taking
+ * the lock and there is a slowpath that does that.
+ *
+ * If true, start will be set to the (even) sequence count read.
+ *
+ * Return: true when a read critical section is started.
+ */
+#define raw_seqcount_try_begin(s, start) \
+({ \
+ start = raw_read_seqcount(s); \
+ !(start & 1); \
+})
+
+/**
* raw_seqcount_begin() - begin a seqcount_t read critical section w/o
* lockdep and w/o counter stabilization
* @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
|