From mboxrd@z Thu Jan 1 00:00:00 1970 From: mathieu.desnoyers@efficios.com (Mathieu Desnoyers) Date: Tue, 23 Aug 2016 23:44:45 -0400 Subject: [lttng-dev] [PATCH latency-tracker] Fix: use local ops for freelist per-cpu counter Message-ID: <1472010285-30868-1-git-send-email-mathieu.desnoyers@efficios.com> Signed-off-by: Mathieu Desnoyers --- tracker_private.h | 3 ++- wrapper/freelist-ll.h | 21 +++++++++++++++------ 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/tracker_private.h b/tracker_private.h index 03386b8..fc27f80 100644 --- a/tracker_private.h +++ b/tracker_private.h @@ -7,6 +7,7 @@ #include #include +#include //#include "wrapper/ht.h" //#include "rculfhash-internal.h" @@ -18,7 +19,7 @@ struct numa_pool { }; struct per_cpu_ll { - int current_count; + local_t current_count; struct numa_pool *pool; struct llist_head llist; }; diff --git a/wrapper/freelist-ll.h b/wrapper/freelist-ll.h index 5e4d18e..44db722 100644 --- a/wrapper/freelist-ll.h +++ b/wrapper/freelist-ll.h @@ -242,8 +242,8 @@ int free_per_cpu_llist(struct latency_tracker *tracker) if (!list) continue; cnt = free_event_list(list); - printk("freed %d on cpu %d (%d)\n", cnt, cpu, - ll->current_count); + printk("freed %d on cpu %d (%ld)\n", cnt, cpu, + local_read(&ll->current_count)); total_cnt += cnt; } @@ -284,10 +284,14 @@ struct llist_node *per_cpu_get(struct latency_tracker *tracker) struct per_cpu_ll *ll; ll = lttng_this_cpu_ptr(tracker->per_cpu_ll); + /* + * Decrement the current count after we successfully remove an + * element from the list. + */ node = llist_del_first(&ll->llist); if (node) { - ll->current_count--; - WARN_ON_ONCE(ll->current_count < 0); + local_dec(&ll->current_count); + WARN_ON_ONCE(local_read(&ll->current_count) < 0); return node; } return llist_del_first(&ll->pool->llist); @@ -336,12 +340,17 @@ void __wrapper_freelist_put_event(struct latency_tracker *tracker, if (e->pool != ll->pool) { // printk("DEBUG cross-pool put_event\n"); llist_add(&e->llist, &ll->pool->llist); - } else if (ll->current_count < FREELIST_PERCPU_CACHE) { + } else if (local_read(&ll->current_count) < FREELIST_PERCPU_CACHE) { /* * Fill our local cache if needed. + * We need to increment current_count before we add the + * element to the list, because when we successfully + * remove an element from the list, we expect that the + * counter is never negative. An interrupt can observe + * the intermediate state. */ + local_inc(&ll->current_count); llist_add(&e->llist, &ll->llist); - ll->current_count++; } else { /* * Add to our NUMA pool. -- 2.1.4