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dpif-netdev: Make datapath and flow stats atomic.

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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.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ethan Jackson <ethan@nicira.com>
This commit is contained in:
Daniele Di Proietto
2015-04-07 20:02:14 +01:00
committed by Ethan Jackson
parent 60fc3b7ba4
commit eb94da30ae
1 changed files with 53 additions and 19 deletions
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72
lib/dpif-netdev.c
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@@ -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_llong used; /* Last used time, in monotonic msecs. */
atomic_ullong packet_count; /* Number of packets matched. */
atomic_ullong 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_ullong n[DP_N_STATS];
};
/* PMD: Poll modes drivers. PMD accesses devices via polling to eliminate
@@ -746,6 +746,21 @@ dpif_netdev_destroy(struct dpif *dpif)
return 0;
}
/* Add 'n' to the atomic variable 'var' non-atomically and using relaxed
* load/store semantics. While the increment is not atomic, the load and
* store operations are, making it impossible to read inconsistent values.
*
* This is used to update thread local stats counters. */
static void
non_atomic_ullong_add(atomic_ullong *var, unsigned long long n)
{
unsigned long long tmp;
atomic_read_relaxed(var, &tmp);
tmp += n;
atomic_store_relaxed(var, tmp);
}
static int
dpif_netdev_get_stats(const struct dpif *dpif, struct dpif_dp_stats *stats)
{
@@ -754,10 +769,15 @@ 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 +1565,24 @@ 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;
unsigned long long n;
long long used;
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, &used);
stats->used = used;
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 +2709,22 @@ 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 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_store_relaxed(&netdev_flow->stats.used, now);
non_atomic_ullong_add(&netdev_flow->stats.packet_count, cnt);
non_atomic_ullong_add(&netdev_flow->stats.byte_count, size);
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;
non_atomic_ullong_add(&pmd->stats.n[type], cnt);
}
static int