Merge branch 'xsk-the-lost-bits-from-chapter-iii'

Alexander Lobakin says:

====================
xsk: the lost bits from Chapter III

Before introducing libeth_xdp, we need to add a couple more generic
helpers. Notably:

* 01: add generic loop unrolling hint helpers;
* 04: add helper to get both xdp_desc's DMA address and metadata
  pointer in one go, saving several cycles and hotpath object
  code size in drivers (especially when unrolling).

Bonus:

* 02, 03: convert two drivers which were using custom macros to
  generic unrolled_count() (trivial, no object code changes).
====================

Link: https://patch.msgid.link/20250206182630.3914318-1-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/include/linux/unroll.h b/include/linux/unroll.h
index d42fd6366373..863fb69f6a7e 100644
--- a/include/linux/unroll.h
+++ b/include/linux/unroll.h
@@ -9,6 +9,50 @@
 
 #include <linux/args.h>
 
+#ifdef CONFIG_CC_IS_CLANG
+#define __pick_unrolled(x, y)		_Pragma(#x)
+#elif CONFIG_GCC_VERSION >= 80000
+#define __pick_unrolled(x, y)		_Pragma(#y)
+#else
+#define __pick_unrolled(x, y)		/* not supported */
+#endif
+
+/**
+ * unrolled - loop attributes to ask the compiler to unroll it
+ *
+ * Usage:
+ *
+ * #define BATCH 8
+ *
+ *	unrolled_count(BATCH)
+ *	for (u32 i = 0; i < BATCH; i++)
+ *		// loop body without cross-iteration dependencies
+ *
+ * This is only a hint and the compiler is free to disable unrolling if it
+ * thinks the count is suboptimal and may hurt performance and/or hugely
+ * increase object code size.
+ * Not having any cross-iteration dependencies (i.e. when iter x + 1 depends
+ * on what iter x will do with variables) is not a strict requirement, but
+ * provides best performance and object code size.
+ * Available only on Clang and GCC 8.x onwards.
+ */
+
+/* Ask the compiler to pick an optimal unroll count, Clang only */
+#define unrolled							\
+	__pick_unrolled(clang loop unroll(enable), /* nothing */)
+
+/* Unroll each @n iterations of the loop */
+#define unrolled_count(n)						\
+	__pick_unrolled(clang loop unroll_count(n), GCC unroll n)
+
+/* Unroll the whole loop */
+#define unrolled_full							\
+	__pick_unrolled(clang loop unroll(full), GCC unroll 65534)
+
+/* Never unroll the loop */
+#define unrolled_none							\
+	__pick_unrolled(clang loop unroll(disable), GCC unroll 1)
+
 #define UNROLL(N, MACRO, args...) CONCATENATE(__UNROLL_, N)(MACRO, args)
 
 #define __UNROLL_0(MACRO, args...)