The commit is pushed to "branch-rh7-3.10.0-693.1.1.vz7.37.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.1.1.vz7.37.4
------>
commit 5a4487bd6d0e4a648b3375083c0e6de1e62c6ca4
Author: Peter Zijlstra <[email protected]>
Date: Fri Sep 15 17:27:36 2017 +0300
seqlock: Introduce raw_read_seqcount_latch()
Because with latches there is a strict data dependency on the seq load
we can avoid the rmb in favour of a read_barrier_depends.
Suggested-by: Ingo Molnar <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
https://jira.sw.ru/browse/PSBM-69081
(cherry picked from commit 7fc26327b75685f37f58d64bdb061460f834f80d)
Signed-off-by: Andrey Ryabinin <[email protected]>
---
include/linux/seqlock.h | 8 ++++++--
kernel/time/timekeeping.c | 2 +-
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index ee088ed..9d89970 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -34,6 +34,7 @@
#include <linux/spinlock.h>
#include <linux/preempt.h>
+#include <linux/compiler.h>
#include <asm/processor.h>
/*
@@ -170,6 +171,10 @@ static inline int read_seqcount_retry(const seqcount_t *s,
unsigned start)
return __read_seqcount_retry(s, start);
}
+static inline int raw_read_seqcount_latch(seqcount_t *s)
+{
+ return lockless_dereference(s->sequence);
+}
/**
* raw_write_seqcount_latch - redirect readers to even/odd copy
@@ -222,8 +227,7 @@ static inline int read_seqcount_retry(const seqcount_t *s,
unsigned start)
* unsigned seq, idx;
*
* do {
- * seq = latch->seq;
- * smp_rmb();
+ * seq = lockless_dereference(latch->seq);
*
* idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 8e5b950..d99c890 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -292,7 +292,7 @@ static __always_inline u64 __ktime_get_fast_ns(struct
tk_fast *tkf)
u64 now;
do {
- seq = raw_read_seqcount(&tkf->seq);
+ seq = raw_read_seqcount_latch(&tkf->seq);
tkr = tkf->base + (seq & 0x01);
now = ktime_to_ns(tkr->base) + timekeeping_get_ns(tkr);
} while (read_seqcount_retry(&tkf->seq, seq));
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