[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCHv6 3/3] p2m: convert p2m rwlock to percpu rwlock
The per domain p2m read lock suffers from significant contention when performance multi-queue block or network IO due to the parallel grant map/unmaps/copies occuring on the DomU's p2m. On multi-socket systems, the contention results in the locked compare swap operation failing frequently which results in a tight loop of retries of the compare swap operation. As the coherency fabric can only support a specific rate of compare swap operations for a particular data location then taking the read lock itself becomes a bottleneck for p2m operations. Percpu rwlock p2m performance with the same configuration is approximately 64 gbit/s vs the 48 gbit/s with grant table percpu rwlocks only. Oprofile was used to determine the initial overhead of the read-write locks and to confirm the overhead was dramatically reduced by the percpu rwlocks. Note: altp2m users will not achieve a gain if they take an altp2m read lock simultaneously with the main p2m lock. Signed-off-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx> -- Changes since v5: - None Changes since v4: - None Changes since v3: - None Changes since v2 - Updated local percpu rwlock initialisation --- xen/arch/x86/mm/mm-locks.h | 12 +++++++----- xen/arch/x86/mm/p2m.c | 1 + xen/include/asm-x86/mm.h | 2 +- 3 files changed, 9 insertions(+), 6 deletions(-) diff --git a/xen/arch/x86/mm/mm-locks.h b/xen/arch/x86/mm/mm-locks.h index 76c7217..8a40986 100644 --- a/xen/arch/x86/mm/mm-locks.h +++ b/xen/arch/x86/mm/mm-locks.h @@ -31,6 +31,8 @@ DECLARE_PER_CPU(int, mm_lock_level); #define __get_lock_level() (this_cpu(mm_lock_level)) +DECLARE_PERCPU_RWLOCK_GLOBAL(p2m_percpu_rwlock); + static inline void mm_lock_init(mm_lock_t *l) { spin_lock_init(&l->lock); @@ -99,7 +101,7 @@ static inline void _mm_enforce_order_lock_post(int level, int *unlock_level, static inline void mm_rwlock_init(mm_rwlock_t *l) { - rwlock_init(&l->lock); + percpu_rwlock_resource_init(&l->lock, p2m_percpu_rwlock); l->locker = -1; l->locker_function = "nobody"; l->unlock_level = 0; @@ -115,7 +117,7 @@ static inline void _mm_write_lock(mm_rwlock_t *l, const char *func, int level) if ( !mm_write_locked_by_me(l) ) { __check_lock_level(level); - write_lock(&l->lock); + percpu_write_lock(p2m_percpu_rwlock, &l->lock); l->locker = get_processor_id(); l->locker_function = func; l->unlock_level = __get_lock_level(); @@ -131,20 +133,20 @@ static inline void mm_write_unlock(mm_rwlock_t *l) l->locker = -1; l->locker_function = "nobody"; __set_lock_level(l->unlock_level); - write_unlock(&l->lock); + percpu_write_unlock(p2m_percpu_rwlock, &l->lock); } static inline void _mm_read_lock(mm_rwlock_t *l, int level) { __check_lock_level(level); - read_lock(&l->lock); + percpu_read_lock(p2m_percpu_rwlock, &l->lock); /* There's nowhere to store the per-CPU unlock level so we can't * set the lock level. */ } static inline void mm_read_unlock(mm_rwlock_t *l) { - read_unlock(&l->lock); + percpu_read_unlock(p2m_percpu_rwlock, &l->lock); } /* This wrapper uses the line number to express the locking order below */ diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index ed0bbd7..a45ee35 100644 --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -54,6 +54,7 @@ boolean_param("hap_2mb", opt_hap_2mb); #undef page_to_mfn #define page_to_mfn(_pg) _mfn(__page_to_mfn(_pg)) +DEFINE_PERCPU_RWLOCK_GLOBAL(p2m_percpu_rwlock); /* Init the datastructures for later use by the p2m code */ static int p2m_initialise(struct domain *d, struct p2m_domain *p2m) diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h index de3f973..7598414 100644 --- a/xen/include/asm-x86/mm.h +++ b/xen/include/asm-x86/mm.h @@ -584,7 +584,7 @@ typedef struct mm_lock { } mm_lock_t; typedef struct mm_rwlock { - rwlock_t lock; + percpu_rwlock_t lock; int unlock_level; int recurse_count; int locker; /* CPU that holds the write lock */ -- 1.7.12.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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