[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCHv11 2/4] gnttab: introduce maptrack lock
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 <msw@xxxxxxxxxx>. Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> --- 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 d91661b..e0ac16f 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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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