[PATCH iwl-next 01/12] libeth: add cacheline / struct alignment helpers

[Alexander Lobakin]

Following the latest netdev trend, i.e. effective and usage-based field
cacheline placement, add helpers to group and then assert struct fields
by cachelines.
For 64-bit with 64-byte cachelines, the assertions are more strict as
the size can then be easily predicted. For the rest, just make sure
they don't cross the specified bound.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
 scripts/kernel-doc         |   1 +
 include/net/libeth/cache.h | 100 +++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 include/net/libeth/cache.h

diff --git a/scripts/kernel-doc b/scripts/kernel-doc
index 95a59ac78f82..d0cf9a2d82de 100755
--- a/scripts/kernel-doc
+++ b/scripts/kernel-doc
@@ -1155,6 +1155,7 @@ sub dump_struct($$) {
         $members =~ s/\bstruct_group_attr\s*\(([^,]*,){2}/STRUCT_GROUP(/gos;
         $members =~ s/\bstruct_group_tagged\s*\(([^,]*),([^,]*),/struct $1 $2; STRUCT_GROUP(/gos;
         $members =~ s/\b__struct_group\s*\(([^,]*,){3}/STRUCT_GROUP(/gos;
+        $members =~ s/\blibeth_cacheline_group\s*\(([^,]*,)/struct { } $1; STRUCT_GROUP(/gos;
         $members =~ s/\bSTRUCT_GROUP(\(((?:(?>[^)(]+)|(?1))*)\))[^;]*;/$2/gos;
 
         my $args = qr{([^,)]+)};
diff --git a/include/net/libeth/cache.h b/include/net/libeth/cache.h
new file mode 100644
index 000000000000..5579240913d2
--- /dev/null
+++ b/include/net/libeth/cache.h
@@ -0,0 +1,100 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (C) 2024 Intel Corporation */
+
+#ifndef __LIBETH_CACHE_H
+#define __LIBETH_CACHE_H
+
+#include <linux/cache.h>
+
+/* ``__aligned_largest`` is architecture-dependent. Get the actual alignment */
+#define ___LIBETH_LARGEST_ALIGN						   \
+	sizeof(struct { long __UNIQUE_ID(long_); } __aligned_largest)
+#define __LIBETH_LARGEST_ALIGN						   \
+	(___LIBETH_LARGEST_ALIGN > SMP_CACHE_BYTES ?			   \
+	 ___LIBETH_LARGEST_ALIGN : SMP_CACHE_BYTES)
+#define __LIBETH_LARGEST_ALIGNED(sz)					   \
+	ALIGN(sz, __LIBETH_LARGEST_ALIGN)
+
+#define __libeth_cacheline_group_begin(grp)				   \
+	__cacheline_group_begin(grp) __aligned(__LIBETH_LARGEST_ALIGN)
+#define __libeth_cacheline_group_end(grp)				   \
+	__cacheline_group_end(grp) __aligned(sizeof(long))
+
+/**
+ * libeth_cacheline_group - declare a cacheline-aligned field group
+ * @grp: name of the group (usually 'read_mostly', 'read_write', or 'cold')
+ * @...: struct fields inside the group
+ *
+ * Note that the whole group is cacheline-aligned, but the end marker is
+ * aligned to long, so that you pass the (almost) actual field size sum to
+ * the assertion macros below instead of CL-aligned values.
+ * Each cacheline group must be described in struct's kernel-doc.
+ */
+#define libeth_cacheline_group(grp, ...)				   \
+	struct_group(grp,						   \
+		__libeth_cacheline_group_begin(grp);			   \
+		__VA_ARGS__						   \
+		__libeth_cacheline_group_end(grp);			   \
+	)
+
+/**
+ * libeth_cacheline_group_assert - make sure cacheline group size is expected
+ * @type: type of the structure containing the group
+ * @grp: group name inside the struct
+ * @sz: expected group size
+ */
+#if defined(CONFIG_64BIT) && SMP_CACHE_BYTES == 64
+#define libeth_cacheline_group_assert(type, grp, sz)			   \
+	static_assert(offsetof(type, __cacheline_group_end__##grp) -	   \
+		      offsetofend(type, __cacheline_group_begin__##grp) == \
+		      (sz))
+#define __libeth_cacheline_struct_assert(type, sz)			   \
+	static_assert(sizeof(type) == (sz))
+#else /* !CONFIG_64BIT || SMP_CACHE_BYTES != 64 */
+#define libeth_cacheline_group_assert(type, grp, sz)			   \
+	static_assert(offsetof(type, __cacheline_group_end__##grp) -	   \
+		      offsetofend(type, __cacheline_group_begin__##grp) <= \
+		      (sz))
+#define __libeth_cacheline_struct_assert(type, sz)			   \
+	static_assert(sizeof(type) <= (sz))
+#endif /* !CONFIG_64BIT || SMP_CACHE_BYTES != 64 */
+
+#define __libeth_cls1(sz1)						   \
+	__LIBETH_LARGEST_ALIGNED(sz1)
+#define __libeth_cls2(sz1, sz2)						   \
+	(__LIBETH_LARGEST_ALIGNED(sz1) + __LIBETH_LARGEST_ALIGNED(sz2))
+#define __libeth_cls3(sz1, sz2, sz3)					   \
+	(__LIBETH_LARGEST_ALIGNED(sz1) + __LIBETH_LARGEST_ALIGNED(sz2) +   \
+	 __LIBETH_LARGEST_ALIGNED(sz3))
+#define __libeth_cls(...)						   \
+	CONCATENATE(__libeth_cls, COUNT_ARGS(__VA_ARGS__))(__VA_ARGS__)
+
+/**
+ * libeth_cacheline_struct_assert - make sure CL-based struct size is expected
+ * @type: type of the struct
+ * @...: from 1 to 3 CL group sizes (read-mostly, read-write, cold)
+ *
+ * When a struct contains several CL groups, it's difficult to predict its size
+ * on different architectures. The macro instead takes sizes of all of the
+ * groups the structure contains and generates the final struct size.
+ */
+#define libeth_cacheline_struct_assert(type, ...)			   \
+	__libeth_cacheline_struct_assert(type, __libeth_cls(__VA_ARGS__)); \
+	static_assert(__alignof(type) >= __LIBETH_LARGEST_ALIGN)
+
+/**
+ * libeth_cacheline_set_assert - make sure CL-based struct layout is expected
+ * @type: type of the struct
+ * @ro: expected size of the read-mostly group
+ * @rw: expected size of the read-write group
+ * @c: expected size of the cold group
+ *
+ * Check that each group size is expected and then do final struct size check.
+ */
+#define libeth_cacheline_set_assert(type, ro, rw, c)			   \
+	libeth_cacheline_group_assert(type, read_mostly, ro);		   \
+	libeth_cacheline_group_assert(type, read_write, rw);		   \
+	libeth_cacheline_group_assert(type, cold, c);			   \
+	libeth_cacheline_struct_assert(type, ro, rw, c)
+
+#endif /* __LIBETH_CACHE_H */
-- 
2.45.1