#include "random.h"
#include "shash.h"
#include "sset.h"
+#include "timeval.h"
#include "unaligned.h"
#include "util.h"
#include "vlog.h"
static void dpif_linux_flow_get_stats(const struct dpif_linux_flow *,
struct dpif_flow_stats *);
+/* Packet drop monitoring.
+ *
+ * When kernel-to-user Netlink buffers overflow, the kernel notifies us that
+ * one or more packets were dropped, but it doesn't tell us anything about
+ * those packets. However, the administrator really wants to know. So we do
+ * the next best thing, and keep track of the top sources of packets received
+ * on each kernel-to-user channel, since the top sources are those that will
+ * cause the buffers to overflow.
+ *
+ * We use a variation on the "Space-Saving" algorithm in Metwally et al.,
+ * "Efficient Computation of Frequent and Top-k Elements in Data Streams", ACM
+ * Transactions on Database Systems 31:3 (2006). This algorithm yields
+ * perfectly accurate results when the data stream's unique values (in this
+ * case, port numbers) fit into our data structure, and degrades gracefully
+ * even for challenging distributions (e.g. Zipf).
+ *
+ * Our implementation is very simple, without any of the special flourishes
+ * described in the paper. It avoids the need to use a hash for lookup by
+ * keeping the constant factor (N_SKETCHES) very small. The error calculations
+ * in the paper make it sound like the results should still be satisfactory.
+ *
+ * "space-saving" and "Metwally" seem like awkward names for data structures,
+ * so we call this a "sketch" even though technically that's a different sort
+ * of summary structure.
+ */
+
+/* One of N_SKETCHES counting elements per channel in the Metwally
+ * "space-saving" algorithm. */
+enum { N_SKETCHES = 8 }; /* Number of elements per channel. */
+struct dpif_sketch {
+ uint32_t port_no; /* Port number. */
+ unsigned int hits; /* Number of hits. */
+ unsigned int error; /* Upper bound on error in 'hits'. */
+};
+
+/* One of N_CHANNELS channels per dpif between the kernel and userspace. */
struct dpif_channel {
- struct nl_sock *sock;
+ struct nl_sock *sock; /* Netlink socket. */
+ struct dpif_sketch sketches[N_SKETCHES]; /* From max to min 'hits'. */
+ long long int last_poll; /* Last time this channel was polled. */
};
+static void update_sketch(struct dpif_channel *, uint32_t port_no);
+static void scale_sketches(struct dpif *);
+static void report_loss(struct dpif *, struct dpif_channel *);
+
+/* Interval, in milliseconds, at which to scale down the sketch values by a
+ * factor of 2. The Metwally algorithm doesn't do this, which makes sense in
+ * the context it assumes, but in our situation we ought to weight recent data
+ * more heavily than old data, so in my opinion this is reasonable. */
+#define SCALE_INTERVAL (60 * 1000)
+
/* Datapath interface for the openvswitch Linux kernel module. */
struct dpif_linux {
struct dpif dpif;
struct dpif_channel channels[N_CHANNELS];
uint32_t ready_mask; /* 1-bit for each sock with unread messages. */
int epoll_fd; /* epoll fd that includes channel socks. */
+ long long int next_scale; /* Next time to scale down the sketches. */
/* Change notification. */
struct sset changed_ports; /* Ports that have changed. */
};
static struct vlog_rate_limit error_rl = VLOG_RATE_LIMIT_INIT(9999, 5);
-static struct vlog_rate_limit enobufs_rl = VLOG_RATE_LIMIT_INIT(60, 5);
/* Generic Netlink family numbers for OVS. */
static int ovs_datapath_family;
dpif_init(&dpif->dpif, &dpif_linux_class, dp->name,
dp->dp_ifindex, dp->dp_ifindex);
+ dpif->next_scale = LLONG_MAX;
+
dpif->dp_ifindex = dp->dp_ifindex;
sset_init(&dpif->changed_ports);
*dpifp = &dpif->dpif;
nl_sock_destroy(ch->sock);
ch->sock = NULL;
}
+ dpif->next_scale = LLONG_MAX;
}
static void
}
static void
-dpif_linux_run(struct dpif *dpif OVS_UNUSED)
+dpif_linux_run(struct dpif *dpif_)
{
+ struct dpif_linux *dpif = dpif_linux_cast(dpif_);
+
+ if (time_msec() >= dpif->next_scale) {
+ dpif->next_scale = time_msec() + SCALE_INTERVAL;
+ scale_sketches(dpif_);
+ }
+
if (nln) {
nln_run(nln);
}
destroy_channels(dpif);
return error;
}
+
+ memset(ch->sketches, 0, sizeof ch->sketches);
+ ch->last_poll = LLONG_MIN;
}
dpif->ready_mask = 0;
+ dpif->next_scale = time_msec() + SCALE_INTERVAL;
}
set_upcall_pids(dpif_);
}
error = nl_sock_recv(ch->sock, buf, false);
+ if (error == ENOBUFS) {
+ /* ENOBUFS typically means that we've received so many
+ * packets that the buffer overflowed. Try again
+ * immediately because there's almost certainly a packet
+ * waiting for us. */
+ report_loss(dpif_, ch);
+ continue;
+ }
+
+ ch->last_poll = time_msec();
if (error) {
- if (error == ENOBUFS) {
- /* ENOBUFS typically means that we've received so many
- * packets that the buffer overflowed. Try again
- * immediately because there's almost certainly a packet
- * waiting for us. */
- VLOG_ERR_RL(&enobufs_rl, "%s: lost packet with hash %d",
- dpif_name(dpif_), dpif->ready_mask);
- continue;
- }
if (error == EAGAIN) {
break;
}
error = parse_odp_packet(buf, upcall, &dp_ifindex);
if (!error && dp_ifindex == dpif->dp_ifindex) {
+ const struct nlattr *in_port;
+
+ in_port = nl_attr_find__(upcall->key, upcall->key_len,
+ OVS_KEY_ATTR_IN_PORT);
+ if (in_port) {
+ update_sketch(ch, nl_attr_get_u32(in_port));
+ }
return 0;
}
if (error) {
stats->used = flow->used ? get_32aligned_u64(flow->used) : 0;
stats->tcp_flags = flow->tcp_flags ? *flow->tcp_flags : 0;
}
+\f
+/* Metwally "space-saving" algorithm implementation. */
+
+/* Updates 'ch' to record that a packet was received on 'port_no'. */
+static void
+update_sketch(struct dpif_channel *ch, uint32_t port_no)
+{
+ struct dpif_sketch *sk;
+
+ /* Find an existing counting element for 'port_no' or, if none, replace the
+ * counting element with the fewest hits by 'port_no'. */
+ for (sk = ch->sketches; ; sk++) {
+ if (port_no == sk->port_no) {
+ break;
+ } else if (sk == &ch->sketches[N_SKETCHES - 1]) {
+ sk->port_no = port_no;
+ sk->error = sk->hits;
+ break;
+ }
+ }
+
+ /* Increment the hit count, then re-sort the counting elements (usually
+ * nothing needs to be done). */
+ sk->hits++;
+ while (sk > ch->sketches && sk[-1].hits > sk->hits) {
+ struct dpif_sketch tmp = sk[-1];
+ sk[-1] = *sk;
+ *sk = tmp;
+ sk--;
+ }
+}
+
+/* Divide the counts of all the the counting elements in 'dpif' by 2. See the
+ * comment on SCALE_INTERVAL. */
+static void
+scale_sketches(struct dpif *dpif_)
+{
+ struct dpif_linux *dpif = dpif_linux_cast(dpif_);
+ struct dpif_channel *ch;
+
+ for (ch = dpif->channels; ch < &dpif->channels[N_CHANNELS]; ch++) {
+ struct dpif_sketch *sk;
+
+ for (sk = ch->sketches; sk < &ch->sketches[N_SKETCHES]; sk++) {
+ sk->hits /= 2;
+ sk->error /= 2;
+ }
+ }
+}
+
+/* Logs information about a packet that was recently lost in 'ch' (in
+ * 'dpif_'). */
+static void
+report_loss(struct dpif *dpif_, struct dpif_channel *ch)
+{
+ struct dpif_linux *dpif = dpif_linux_cast(dpif_);
+ static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 5);
+ struct dpif_sketch *sk;
+ struct ds s;
+
+ if (VLOG_DROP_ERR(&rl)) {
+ return;
+ }
+
+ ds_init(&s);
+ if (ch->last_poll != LLONG_MIN) {
+ ds_put_format(&s, " (last polled %lld ms ago)",
+ time_msec() - ch->last_poll);
+ }
+ ds_put_cstr(&s, ", most frequent sources are");
+ for (sk = ch->sketches; sk < &ch->sketches[N_SKETCHES]; sk++) {
+ if (sk->hits) {
+ struct dpif_port port;
+
+ ds_put_format(&s, " %"PRIu32, sk->port_no);
+ if (!dpif_port_query_by_number(dpif_, sk->port_no, &port)) {
+ ds_put_format(&s, "(%s)", port.name);
+ dpif_port_destroy(&port);
+ }
+ if (sk->error) {
+ ds_put_format(&s, ": %u to %u,",
+ sk->hits - sk->error, sk->hits);
+ } else {
+ ds_put_format(&s, ": %u,", sk->hits);
+ }
+ }
+ }
+ ds_chomp(&s, ',');
+
+ VLOG_ERR("%s: lost packet on channel %d%s",
+ dpif_name(dpif_), ch - dpif->channels, ds_cstr(&s));
+ ds_destroy(&s);
+}
projects / openvswitch / commitdiff