Split grant table lock into two separate locks. One to protect
maptrack state (maptrack_lock) and one for everything else (lock).
Based on a patch originally by Matt Wilson <m...@amazon.com>.
Signed-off-by: David Vrabel <david.vra...@citrix.com>
---
docs/misc/grant-tables.txt | 9 +++++++++
xen/common/grant_table.c | 9 +++++----
xen/include/xen/grant_table.h | 2 ++
3 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/docs/misc/grant-tables.txt b/docs/misc/grant-tables.txt
index 2a3f591..83b3454 100644
--- a/docs/misc/grant-tables.txt
+++ b/docs/misc/grant-tables.txt
@@ -87,6 +87,7 @@ is complete.
inconsistent grant table state such as current
version, partially initialized active table
pages,
etc.
+ grant_table->maptrack_lock : spinlock used to protect the maptrack state
active_grant_entry->lock : spinlock used to serialize modifications to
active entries
@@ -94,6 +95,14 @@ is complete.
that access members of struct grant_table must acquire the lock
around critical sections.
+ The maptrack state is protected by its own spinlock. Any access (read
+ or write) of struct grant_table members that have a "maptrack_"
+ prefix must be made while holding the maptrack lock. The maptrack
+ state can be rapidly modified under some workloads, and the critical
+ sections are very small, thus we use a spinlock to protect them.
+
+ The maptrack lock may be locked while holding the grant table lock.
+
Active entries are obtained by calling active_entry_acquire(gt, ref).
This function returns a pointer to the active entry after locking its
spinlock. The caller must hold the grant table lock for the gt in
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index bb90627..fee34ee 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -288,10 +288,10 @@ static inline void
put_maptrack_handle(
struct grant_table *t, int handle)
{
- spin_lock(&t->lock);
+ spin_lock(&t->maptrack_lock);
maptrack_entry(t, handle).ref = t->maptrack_head;
t->maptrack_head = handle;
- spin_unlock(&t->lock);
+ spin_unlock(&t->maptrack_lock);
}
static inline int
@@ -303,7 +303,7 @@ get_maptrack_handle(
struct grant_mapping *new_mt;
unsigned int new_mt_limit, nr_frames;
- spin_lock(&lgt->lock);
+ spin_lock(&lgt->maptrack_lock);
while ( unlikely((handle = __get_maptrack_handle(lgt)) == -1) )
{
@@ -332,7 +332,7 @@ get_maptrack_handle(
nr_frames + 1);
}
- spin_unlock(&lgt->lock);
+ spin_unlock(&lgt->maptrack_lock);
return handle;
}
@@ -3005,6 +3005,7 @@ grant_table_create(
/* Simple stuff. */
spin_lock_init(&t->lock);
+ spin_lock_init(&t->maptrack_lock);
t->nr_grant_frames = INITIAL_NR_GRANT_FRAMES;
/* Active grant table. */
diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h
index 32f5786..0b35a5e 100644
--- a/xen/include/xen/grant_table.h
+++ b/xen/include/xen/grant_table.h
@@ -82,6 +82,8 @@ struct grant_table {
struct grant_mapping **maptrack;
unsigned int maptrack_head;
unsigned int maptrack_limit;
+ /* Lock protecting the maptrack page list, head, and limit */
+ spinlock_t maptrack_lock;
/* Lock protecting updates to active and shared grant tables. */
spinlock_t lock;
/* The defined versions are 1 and 2. Set to 0 if we don't know
--
1.7.10.4
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