Author: mjg
Date: Sat Jul 25 10:29:48 2020
New Revision: 363516
URL: https://svnweb.freebsd.org/changeset/base/363516
Log:
seqc: add a sleepable variant and convert some routines to macros
This temporarily duplicates some code.
Macro conversion convinces clang to carry predicts into consumers.
Added:
head/sys/sys/_seqc.h (contents, props changed)
Modified:
head/sys/sys/seqc.h
Added: head/sys/sys/_seqc.h
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/sys/sys/_seqc.h Sat Jul 25 10:29:48 2020 (r363516)
@@ -0,0 +1,11 @@
+/*-
+ * This file is in the public domain.
+ */
+/* $FreeBSD$ */
+
+#ifndef _SYS__SEQC_H_
+#define _SYS__SEQC_H_
+
+typedef uint32_t seqc_t;
+
+#endif /* _SYS__SEQC_H */
Modified: head/sys/sys/seqc.h
==============================================================================
--- head/sys/sys/seqc.h Sat Jul 25 09:28:38 2020 (r363515)
+++ head/sys/sys/seqc.h Sat Jul 25 10:29:48 2020 (r363516)
@@ -36,7 +36,7 @@
/*
* seqc_t may be included in structs visible to userspace
*/
-typedef uint32_t seqc_t;
+#include <sys/_seqc.h>
#ifdef _KERNEL
@@ -45,13 +45,15 @@ typedef uint32_t seqc_t;
#include <machine/cpu.h>
-static __inline bool
-seqc_in_modify(seqc_t seqcp)
-{
+/*
+ * Predicts from inline functions are not honored by clang.
+ */
+#define seqc_in_modify(seqc) ({ \
+ seqc_t __seqc = (seqc); \
+ \
+ __predict_false(__seqc & 1); \
+})
- return (seqcp & 1);
-}
-
static __inline void
seqc_write_begin(seqc_t *seqcp)
{
@@ -86,7 +88,7 @@ seqc_read(const seqc_t *seqcp)
for (;;) {
ret = seqc_read_any(seqcp);
- if (__predict_false(seqc_in_modify(ret))) {
+ if (seqc_in_modify(ret)) {
cpu_spinwait();
continue;
}
@@ -96,19 +98,38 @@ seqc_read(const seqc_t *seqcp)
return (ret);
}
-static __inline bool
-seqc_consistent_nomb(const seqc_t *seqcp, seqc_t oldseqc)
+#define seqc_consistent_nomb(seqcp, oldseqc) ({ \
+ const seqc_t *__seqcp = (seqcp); \
+ seqc_t __oldseqc = (oldseqc); \
+ \
+ MPASS(!(seqc_in_modify(__oldseqc))); \
+ __predict_true(*__seqcp == __oldseqc); \
+})
+
+#define seqc_consistent(seqcp, oldseqc) ({ \
+ atomic_thread_fence_acq(); \
+ seqc_consistent_nomb(seqcp, oldseqc); \
+})
+
+/*
+ * Variant which does not critical enter/exit.
+ */
+static __inline void
+seqc_sleepable_write_begin(seqc_t *seqcp)
{
- return (*seqcp == oldseqc);
+ MPASS(!seqc_in_modify(*seqcp));
+ *seqcp += 1;
+ atomic_thread_fence_rel();
}
-static __inline bool
-seqc_consistent(const seqc_t *seqcp, seqc_t oldseqc)
+static __inline void
+seqc_sleepable_write_end(seqc_t *seqcp)
{
- atomic_thread_fence_acq();
- return (seqc_consistent_nomb(seqcp, oldseqc));
+ atomic_thread_fence_rel();
+ *seqcp += 1;
+ MPASS(!seqc_in_modify(*seqcp));
}
#endif /* _KERNEL */
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