The patch titled
llist: move cpu_relax after cmpxchg
has been added to the -mm tree. Its filename is
llist-move-cpu_relax-after-cmpxchg.patch
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------------------------------------------------------
Subject: llist: move cpu_relax after cmpxchg
From: Huang Ying <ying.huang@xxxxxxxxx>
If the first cmpxchg call succeeds, it is not necessary to use cpu_relax
before cmpxchg. So cpu_relax in a busy loop involving cmpxchg should go
after cmpxchg instead of before that. This patch fixes this in llist.
Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/llist.h | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
diff -puN include/linux/llist.h~llist-move-cpu_relax-after-cmpxchg include/linux/llist.h
--- a/include/linux/llist.h~llist-move-cpu_relax-after-cmpxchg
+++ a/include/linux/llist.h
@@ -156,11 +156,14 @@ static inline void llist_add(struct llis
CHECK_NMI_SAFE_CMPXCHG();
entry = head->first;
- do {
+ for (;;) {
old_entry = entry;
new->next = entry;
+ entry = cmpxchg(&head->first, old_entry, new);
+ if (entry == old_entry)
+ break;
cpu_relax();
- } while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
+ }
}
/**
@@ -178,11 +181,14 @@ static inline void llist_add_batch(struc
CHECK_NMI_SAFE_CMPXCHG();
entry = head->first;
- do {
+ for (;;) {
old_entry = entry;
new_last->next = entry;
+ entry = cmpxchg(&head->first, old_entry, new_first);
+ if (entry == old_entry)
+ break;
cpu_relax();
- } while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
+ }
}
/**
@@ -206,13 +212,16 @@ static inline struct llist_node *llist_d
CHECK_NMI_SAFE_CMPXCHG();
entry = head->first;
- do {
+ for (;;) {
if (entry == NULL)
return NULL;
old_entry = entry;
next = entry->next;
+ entry = cmpxchg(&head->first, old_entry, next);
+ if (entry == old_entry)
+ break;
cpu_relax();
- } while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
+ }
return entry;
}
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
llist-make-all-llist-functions-inline.patch
llist-define-macro-to-check-nmi-safe-cmpxchg.patch
llist-move-cpu_relax-after-cmpxchg.patch
kernel-irq_workc-use-llist-in-irq_work.patch
net-rds-replace-xlist-in-net-rds-xlisth-with-llist.patch
lib-bitmapc-quiet-sparse-noise-about-address-space.patch
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