From: Mikael Pettersson <mikpe@csd.uu.se>
This set of patches changes perfctr's low-level drivers to indicate changes to
the mmap:ed counter state via a unified seqlock mechanism. This cleans up
user-space, enables user-space fast sampling in some previously impossible
cases (x86 w/o TSC), and eliminates a highly unlikely but not impossible
failure case on x86 SMP.
This is a rewrite of a patch originally from David Gibson.
perfctr seqlocks 1/4: common changes
- define write_perfseq_begin/end in <linux/perfctr.h>
- bump version and sync it with current user-space package
Signed-off-by: Mikael Pettersson <mikpe@csd.uu.se>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
drivers/perfctr/version.h | 2 +-
include/linux/perfctr.h | 17 +++++++++++++++++
2 files changed, 18 insertions(+), 1 deletion(-)
diff -puN drivers/perfctr/version.h~perfctr-seqlocks-for-mmaped-state-common drivers/perfctr/version.h
--- 25/drivers/perfctr/version.h~perfctr-seqlocks-for-mmaped-state-common 2005-05-26 22:57:36.000000000 -0700
+++ 25-akpm/drivers/perfctr/version.h 2005-05-26 22:57:36.000000000 -0700
@@ -1 +1 @@
-#define VERSION "2.7.15"
+#define VERSION "2.7.17"
diff -puN include/linux/perfctr.h~perfctr-seqlocks-for-mmaped-state-common include/linux/perfctr.h
--- 25/include/linux/perfctr.h~perfctr-seqlocks-for-mmaped-state-common 2005-05-26 22:57:36.000000000 -0700
+++ 25-akpm/include/linux/perfctr.h 2005-05-26 22:57:36.000000000 -0700
@@ -154,6 +154,23 @@ static inline void perfctr_set_cpus_allo
#endif /* CONFIG_PERFCTR_VIRTUAL */
+/* These routines are identical to write_seqcount_begin() and
+ * write_seqcount_end(), except they take an explicit __u32 rather
+ * than a seqcount_t. That's because this sequence lock is user from
+ * userspace, so we have to pin down the counter's type explicitly to
+ * have a clear ABI. They also omit the SMP write barriers since we
+ * only support mmap() based sampling for self-monitoring tasks.
+ */
+static inline void write_perfseq_begin(__u32 *seq)
+{
+ ++*seq;
+}
+
+static inline void write_perfseq_end(__u32 *seq)
+{
+ ++*seq;
+}
+
#endif /* __KERNEL__ */
#endif /* _LINUX_PERFCTR_H */
_