Did an overhaul of this patch (mainly cleaned up comments and changelog), merged, thanks!
Mathieu commit 2ef1bfb2cb9abb657e077814e272801e197a3c47 Author: Lai Jiangshan <[email protected]> Date: Thu Sep 29 13:47:13 2011 -0400 urcu,defer_rcu: Make defer_rcu encoding more compact for marker When the function changes (and the function is aligned), and only the data is the marker, we can get away with using only 2 pointers rather than 3. [ Edit by Mathieu Desnoyers: patch cleanup, changelog updates ] Signed-off-by: Lai Jiangshan <[email protected]> Signed-off-by: Mathieu Desnoyers <[email protected]> diff --git a/urcu-defer-impl.h b/urcu-defer-impl.h index 4211f7c..34d99c9 100644 --- a/urcu-defer-impl.h +++ b/urcu-defer-impl.h @@ -61,7 +61,9 @@ * Assumes that (void *)-2L is not used often. Used to encode non-aligned * functions and non-aligned data using extra space. * We encode the (void *)-2L fct as: -2L, fct, data. - * We encode the (void *)-2L data as: -2L, fct, data. + * We encode the (void *)-2L data as either: + * fct | DQ_FCT_BIT, data (if fct is aligned), or + * -2L, fct, data (if fct is not aligned). * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order. */ #define DQ_FCT_BIT (1 << 0) @@ -322,14 +324,27 @@ void _defer_rcu(void (*fct)(void *p), void *p) assert(head - CMM_LOAD_SHARED(defer_queue.tail) == 0); } - if (unlikely(defer_queue.last_fct_in != fct)) { + /* + * Encode: + * if the function is not changed and the data is aligned and it is + * not the marker: + * store the data + * otherwise if the function is aligned and its not the marker: + * store the function with DQ_FCT_BIT + * store the data + * otherwise: + * store the marker (DQ_FCT_MARK) + * store the function + * store the data + * + * Decode: see the comments before 'struct defer_queue' + * or the code in rcu_defer_barrier_queue(). + */ + if (unlikely(defer_queue.last_fct_in != fct + || DQ_IS_FCT_BIT(p) + || p == DQ_FCT_MARK)) { defer_queue.last_fct_in = fct; if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) { - /* - * If the function to encode is not aligned or the - * marker, write DQ_FCT_MARK followed by the function - * pointer. - */ _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], DQ_FCT_MARK); _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], @@ -339,17 +354,6 @@ void _defer_rcu(void (*fct)(void *p), void *p) _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], fct); } - } else { - if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) { - /* - * If the data to encode is not aligned or the marker, - * write DQ_FCT_MARK followed by the function pointer. - */ - _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], - DQ_FCT_MARK); - _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], - fct); - } } _CMM_STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p); cmm_smp_wmb(); /* Publish new pointer before head */ -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com _______________________________________________ ltt-dev mailing list [email protected] http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
