A read operation from a non atomic shared value (without external
locking) can return incorrect values. Using the atomic semantics
prevents this from happening.
However:
* No memory barriers are used. We don't need that kind of consistency
for statistics (we use relaxed operations).
* The updates are not atomic, just the loads and stores. This is ok
because there's a single writer.
Suggested-by: Ethan Jackson <et...@nicira.com>
Signed-off-by: Daniele Di Proietto <diproiet...@vmware.com>
---
lib/dpif-netdev.c | 69 ++++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 50 insertions(+), 19 deletions(-)
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index b5cfdcb..a882e9c 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -239,10 +239,10 @@ struct dp_netdev_port {
/* Contained by struct dp_netdev_flow's 'stats' member. */
struct dp_netdev_flow_stats {
- long long int used; /* Last used time, in monotonic msecs. */
- long long int packet_count; /* Number of packets matched. */
- long long int byte_count; /* Number of bytes matched. */
- uint16_t tcp_flags; /* Bitwise-OR of seen tcp_flags values. */
+ ATOMIC(long long) used; /* Last used time, in monotonic msecs. */
+ ATOMIC(long long) packet_count; /* Number of packets matched. */
+ ATOMIC(long long) byte_count; /* Number of bytes matched. */
+ ATOMIC(uint16_t) tcp_flags; /* Bitwise-OR of seen tcp_flags values. */
};
/* A flow in 'dp_netdev_pmd_thread's 'flow_table'.
@@ -338,7 +338,7 @@ static void dp_netdev_actions_free(struct dp_netdev_actions
*);
/* Contained by struct dp_netdev_pmd_thread's 'stats' member. */
struct dp_netdev_pmd_stats {
/* Indexed by DP_STAT_*. */
- unsigned long long int n[DP_N_STATS];
+ ATOMIC(unsigned long long) n[DP_N_STATS];
};
/* PMD: Poll modes drivers. PMD accesses devices via polling to eliminate
@@ -754,10 +754,15 @@ dpif_netdev_get_stats(const struct dpif *dpif, struct
dpif_dp_stats *stats)
stats->n_flows = stats->n_hit = stats->n_missed = stats->n_lost = 0;
CMAP_FOR_EACH (pmd, node, &dp->poll_threads) {
+ unsigned long long n;
stats->n_flows += cmap_count(&pmd->flow_table);
- stats->n_hit += pmd->stats.n[DP_STAT_HIT];
- stats->n_missed += pmd->stats.n[DP_STAT_MISS];
- stats->n_lost += pmd->stats.n[DP_STAT_LOST];
+
+ atomic_read_relaxed(&pmd->stats.n[DP_STAT_HIT], &n);
+ stats->n_hit += n;
+ atomic_read_relaxed(&pmd->stats.n[DP_STAT_MISS], &n);
+ stats->n_missed += n;
+ atomic_read_relaxed(&pmd->stats.n[DP_STAT_LOST], &n);
+ stats->n_lost += n;
}
stats->n_masks = UINT32_MAX;
stats->n_mask_hit = UINT64_MAX;
@@ -1545,13 +1550,23 @@ dp_netdev_pmd_find_flow(const struct
dp_netdev_pmd_thread *pmd,
}
static void
-get_dpif_flow_stats(const struct dp_netdev_flow *netdev_flow,
+get_dpif_flow_stats(const struct dp_netdev_flow *netdev_flow_,
struct dpif_flow_stats *stats)
{
- stats->n_packets = netdev_flow->stats.packet_count;
- stats->n_bytes = netdev_flow->stats.byte_count;
- stats->used = netdev_flow->stats.used;
- stats->tcp_flags = netdev_flow->stats.tcp_flags;
+ struct dp_netdev_flow *netdev_flow;
+ long long n;
+ uint16_t flags;
+
+ netdev_flow = CONST_CAST(struct dp_netdev_flow *, netdev_flow_);
+
+ atomic_read_relaxed(&netdev_flow->stats.packet_count, &n);
+ stats->n_packets = n;
+ atomic_read_relaxed(&netdev_flow->stats.byte_count, &n);
+ stats->n_bytes = n;
+ atomic_read_relaxed(&netdev_flow->stats.used, &n);
+ stats->used = n;
+ atomic_read_relaxed(&netdev_flow->stats.tcp_flags, &flags);
+ stats->tcp_flags = flags;
}
/* Converts to the dpif_flow format, using 'key_buf' and 'mask_buf' for
@@ -2678,19 +2693,35 @@ static void
dp_netdev_flow_used(struct dp_netdev_flow *netdev_flow, int cnt, int size,
uint16_t tcp_flags)
{
- long long int now = time_msec();
+ long long n, now = time_msec();
+ uint16_t flags;
- netdev_flow->stats.used = MAX(now, netdev_flow->stats.used);
- netdev_flow->stats.packet_count += cnt;
- netdev_flow->stats.byte_count += size;
- netdev_flow->stats.tcp_flags |= tcp_flags;
+ atomic_read_relaxed(&netdev_flow->stats.used, &n);
+ n = MAX(now, n);
+ atomic_store_relaxed(&netdev_flow->stats.used, n);
+
+ atomic_read_relaxed(&netdev_flow->stats.packet_count, &n);
+ n += cnt;
+ atomic_store_relaxed(&netdev_flow->stats.packet_count, n);
+
+ atomic_read_relaxed(&netdev_flow->stats.byte_count, &n);
+ n += size;
+ atomic_store_relaxed(&netdev_flow->stats.byte_count, n);
+
+ atomic_read_relaxed(&netdev_flow->stats.tcp_flags, &flags);
+ flags |= tcp_flags;
+ atomic_store_relaxed(&netdev_flow->stats.tcp_flags, flags);
}
static void
dp_netdev_count_packet(struct dp_netdev_pmd_thread *pmd,
enum dp_stat_type type, int cnt)
{
- pmd->stats.n[type] += cnt;
+ unsigned long long n;
+
+ atomic_read_relaxed(&pmd->stats.n[type], &n);
+ n += cnt;
+ atomic_store_relaxed(&pmd->stats.n[type], n);
}
static int
--
2.1.4
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