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dpif-netdev: Add PMD load based sleeping.
Sleep for an incremental amount of time if none of the Rx queues assigned to a PMD have at least half a batch of packets (i.e. 16 pkts) on an polling iteration of the PMD. Upon detecting the threshold of >= 16 pkts on an Rxq, reset the sleep time to zero (i.e. no sleep). Sleep time will be increased on each iteration where the low load conditions remain up to a total of the max sleep time which is set by the user e.g: ovs-vsctl set Open_vSwitch . other_config:pmd-maxsleep=500 The default pmd-maxsleep value is 0, which means that no sleeps will occur and the default behaviour is unchanged from previously. Also add new stats to pmd-perf-show to get visibility of operation e.g. ... - sleep iterations: 153994 ( 76.8 % of iterations) Sleep time (us): 9159399 ( 59 us/iteration avg.) ... Reviewed-by: Robin Jarry <rjarry@redhat.com> Reviewed-by: David Marchand <david.marchand@redhat.com> Signed-off-by: Kevin Traynor <ktraynor@redhat.com> Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
This commit is contained in:
Kevin Traynor
Ilya Maximets
parent
f4c8841351
commit
de3bbdc479
@ -324,5 +324,59 @@ A user can use this option to set a minimum frequency of Rx queue to PMD
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reassignment due to PMD Auto Load Balance. For example, this could be set
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(in min) such that a reassignment is triggered at most every few hours.
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PMD load based sleeping (Experimental)
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--------------------------------------
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PMD threads constantly poll Rx queues which are assigned to them. In order to
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reduce the CPU cycles they use, they can sleep for small periods of time
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when there is no load or very-low load on all the Rx queues they poll.
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This can be enabled by setting the max requested sleep time (in microseconds)
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for a PMD thread::
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$ ovs-vsctl set open_vswitch . other_config:pmd-maxsleep=500
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Non-zero values will be rounded up to the nearest 10 microseconds to avoid
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requesting very small sleep times.
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With a non-zero max value a PMD may request to sleep by an incrementing amount
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of time up to the maximum time. If at any point the threshold of at least half
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a batch of packets (i.e. 16) is received from an Rx queue that the PMD is
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polling is met, the requested sleep time will be reset to 0. At that point no
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sleeps will occur until the no/low load conditions return.
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Sleeping in a PMD thread will mean there is a period of time when the PMD
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thread will not process packets. Sleep times requested are not guaranteed
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and can differ significantly depending on system configuration. The actual
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time not processing packets will be determined by the sleep and processor
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wake-up times and should be tested with each system configuration.
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Sleep time statistics for 10 secs can be seen with::
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$ ovs-appctl dpif-netdev/pmd-stats-clear \
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&& sleep 10 && ovs-appctl dpif-netdev/pmd-perf-show
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Example output, showing that during the last 10 seconds, 76.8% of iterations
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had a sleep of some length. The total amount of sleep time was 9.15 seconds and
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the average sleep time per iteration was 46 microseconds::
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- sleep iterations: 153994 ( 76.8 % of iterations)
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Sleep time (us): 9159399 ( 59 us/iteration avg.)
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Any potential power saving from PMD load based sleeping is dependent on the
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system configuration (e.g. enabling processor C-states) and workloads.
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.. note::
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If there is a sudden spike of packets while the PMD thread is sleeping and
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the processor is in a low-power state it may result in some lost packets or
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extra latency before the PMD thread returns to processing packets at full
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rate.
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.. note::
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By default Linux kernel groups timer expirations and this can add an
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overhead of up to 50 microseconds to a requested timer expiration.
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.. _ovs-vswitchd(8):
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http://openvswitch.org/support/dist-docs/ovs-vswitchd.8.html
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3
NEWS
3
NEWS
@ -30,6 +30,9 @@ Post-v3.0.0
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- Userspace datapath:
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* Add '-secs' argument to appctl 'dpif-netdev/pmd-rxq-show' to show
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the pmd usage of an Rx queue over a configurable time period.
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* Add new experimental PMD load based sleeping feature. PMD threads can
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request to sleep up to a user configured 'pmd-maxsleep' value under
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low load conditions.
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v3.0.0 - 15 Aug 2022
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@ -230,18 +230,26 @@ pmd_perf_format_overall_stats(struct ds *str, struct pmd_perf_stats *s,
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uint64_t tot_iter = histogram_samples(&s->pkts);
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uint64_t idle_iter = s->pkts.bin[0];
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uint64_t busy_iter = tot_iter >= idle_iter ? tot_iter - idle_iter : 0;
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uint64_t sleep_iter = stats[PMD_SLEEP_ITER];
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uint64_t tot_sleep_cycles = stats[PMD_CYCLES_SLEEP];
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ds_put_format(str,
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" Iterations: %12"PRIu64" (%.2f us/it)\n"
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" - Used TSC cycles: %12"PRIu64" (%5.1f %% of total cycles)\n"
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" - idle iterations: %12"PRIu64" (%5.1f %% of used cycles)\n"
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" - busy iterations: %12"PRIu64" (%5.1f %% of used cycles)\n",
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tot_iter, tot_cycles * us_per_cycle / tot_iter,
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" - busy iterations: %12"PRIu64" (%5.1f %% of used cycles)\n"
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" - sleep iterations: %12"PRIu64" (%5.1f %% of iterations)\n"
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" Sleep time (us): %12.0f (%3.0f us/iteration avg.)\n",
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tot_iter,
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(tot_cycles + tot_sleep_cycles) * us_per_cycle / tot_iter,
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tot_cycles, 100.0 * (tot_cycles / duration) / tsc_hz,
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idle_iter,
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100.0 * stats[PMD_CYCLES_ITER_IDLE] / tot_cycles,
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busy_iter,
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100.0 * stats[PMD_CYCLES_ITER_BUSY] / tot_cycles);
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100.0 * stats[PMD_CYCLES_ITER_BUSY] / tot_cycles,
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sleep_iter, tot_iter ? 100.0 * sleep_iter / tot_iter : 0,
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tot_sleep_cycles * us_per_cycle,
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sleep_iter ? (tot_sleep_cycles * us_per_cycle) / sleep_iter : 0);
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if (rx_packets > 0) {
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ds_put_format(str,
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" Rx packets: %12"PRIu64" (%.0f Kpps, %.0f cycles/pkt)\n"
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@ -518,14 +526,15 @@ OVS_REQUIRES(s->stats_mutex)
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void
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pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
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int tx_packets, bool full_metrics)
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int tx_packets, uint64_t sleep_cycles,
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bool full_metrics)
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{
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uint64_t now_tsc = cycles_counter_update(s);
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struct iter_stats *cum_ms;
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uint64_t cycles, cycles_per_pkt = 0;
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char *reason = NULL;
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cycles = now_tsc - s->start_tsc;
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cycles = now_tsc - s->start_tsc - sleep_cycles;
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s->current.timestamp = s->iteration_cnt;
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s->current.cycles = cycles;
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s->current.pkts = rx_packets;
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@ -539,6 +548,11 @@ pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
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histogram_add_sample(&s->cycles, cycles);
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histogram_add_sample(&s->pkts, rx_packets);
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if (sleep_cycles) {
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pmd_perf_update_counter(s, PMD_SLEEP_ITER, 1);
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pmd_perf_update_counter(s, PMD_CYCLES_SLEEP, sleep_cycles);
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}
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if (!full_metrics) {
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return;
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}
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@ -80,6 +80,8 @@ enum pmd_stat_type {
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PMD_CYCLES_ITER_IDLE, /* Cycles spent in idle iterations. */
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PMD_CYCLES_ITER_BUSY, /* Cycles spent in busy iterations. */
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PMD_CYCLES_UPCALL, /* Cycles spent processing upcalls. */
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PMD_SLEEP_ITER, /* Iterations where a sleep has taken place. */
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PMD_CYCLES_SLEEP, /* Total cycles slept to save power. */
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PMD_N_STATS
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};
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@ -408,7 +410,8 @@ void
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pmd_perf_start_iteration(struct pmd_perf_stats *s);
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void
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pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets,
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int tx_packets, bool full_metrics);
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int tx_packets, uint64_t sleep_cycles,
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bool full_metrics);
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/* Formatting the output of commands. */
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@ -171,6 +171,11 @@ static struct odp_support dp_netdev_support = {
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/* Time in microseconds to try RCU quiescing. */
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#define PMD_RCU_QUIESCE_INTERVAL 10000LL
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/* Number of pkts Rx on an interface that will stop pmd thread sleeping. */
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#define PMD_SLEEP_THRESH (NETDEV_MAX_BURST / 2)
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/* Time in uS to increment a pmd thread sleep time. */
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#define PMD_SLEEP_INC_US 10
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struct dpcls {
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struct cmap_node node; /* Within dp_netdev_pmd_thread.classifiers */
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odp_port_t in_port;
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@ -279,6 +284,8 @@ struct dp_netdev {
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atomic_uint32_t emc_insert_min;
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/* Enable collection of PMD performance metrics. */
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atomic_bool pmd_perf_metrics;
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/* Max load based sleep request. */
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atomic_uint64_t pmd_max_sleep;
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/* Enable the SMC cache from ovsdb config */
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atomic_bool smc_enable_db;
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@ -4821,8 +4828,10 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
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uint64_t rebalance_intvl;
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uint8_t cur_rebalance_load;
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uint32_t rebalance_load, rebalance_improve;
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uint64_t pmd_max_sleep, cur_pmd_max_sleep;
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bool log_autolb = false;
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enum sched_assignment_type pmd_rxq_assign_type;
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static bool first_set_config = true;
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tx_flush_interval = smap_get_int(other_config, "tx-flush-interval",
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DEFAULT_TX_FLUSH_INTERVAL);
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@ -4969,6 +4978,19 @@ dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
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bool autolb_state = smap_get_bool(other_config, "pmd-auto-lb", false);
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set_pmd_auto_lb(dp, autolb_state, log_autolb);
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pmd_max_sleep = smap_get_ullong(other_config, "pmd-maxsleep", 0);
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pmd_max_sleep = ROUND_UP(pmd_max_sleep, 10);
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pmd_max_sleep = MIN(PMD_RCU_QUIESCE_INTERVAL, pmd_max_sleep);
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atomic_read_relaxed(&dp->pmd_max_sleep, &cur_pmd_max_sleep);
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if (first_set_config || pmd_max_sleep != cur_pmd_max_sleep) {
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atomic_store_relaxed(&dp->pmd_max_sleep, pmd_max_sleep);
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VLOG_INFO("PMD max sleep request is %"PRIu64" usecs.", pmd_max_sleep);
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VLOG_INFO("PMD load based sleeps are %s.",
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pmd_max_sleep ? "enabled" : "disabled" );
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}
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first_set_config = false;
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return 0;
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}
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@ -6929,6 +6951,7 @@ pmd_thread_main(void *f_)
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int poll_cnt;
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int i;
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int process_packets = 0;
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uint64_t sleep_time = 0;
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poll_list = NULL;
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@ -6989,10 +7012,13 @@ reload:
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ovs_mutex_lock(&pmd->perf_stats.stats_mutex);
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for (;;) {
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uint64_t rx_packets = 0, tx_packets = 0;
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uint64_t time_slept = 0;
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uint64_t max_sleep;
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pmd_perf_start_iteration(s);
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atomic_read_relaxed(&pmd->dp->smc_enable_db, &pmd->ctx.smc_enable_db);
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atomic_read_relaxed(&pmd->dp->pmd_max_sleep, &max_sleep);
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for (i = 0; i < poll_cnt; i++) {
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@ -7011,6 +7037,9 @@ reload:
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dp_netdev_process_rxq_port(pmd, poll_list[i].rxq,
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poll_list[i].port_no);
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rx_packets += process_packets;
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if (process_packets >= PMD_SLEEP_THRESH) {
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sleep_time = 0;
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}
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}
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if (!rx_packets) {
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@ -7018,7 +7047,30 @@ reload:
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* Check if we need to send something.
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* There was no time updates on current iteration. */
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pmd_thread_ctx_time_update(pmd);
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tx_packets = dp_netdev_pmd_flush_output_packets(pmd, false);
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tx_packets = dp_netdev_pmd_flush_output_packets(pmd,
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max_sleep && sleep_time
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? true : false);
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}
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if (max_sleep) {
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/* Check if a sleep should happen on this iteration. */
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if (sleep_time) {
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struct cycle_timer sleep_timer;
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cycle_timer_start(&pmd->perf_stats, &sleep_timer);
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xnanosleep_no_quiesce(sleep_time * 1000);
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time_slept = cycle_timer_stop(&pmd->perf_stats, &sleep_timer);
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pmd_thread_ctx_time_update(pmd);
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}
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if (sleep_time < max_sleep) {
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/* Increase sleep time for next iteration. */
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sleep_time += PMD_SLEEP_INC_US;
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} else {
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sleep_time = max_sleep;
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}
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} else {
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/* Reset sleep time as max sleep policy may have been changed. */
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sleep_time = 0;
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}
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/* Do RCU synchronization at fixed interval. This ensures that
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@ -7058,7 +7110,7 @@ reload:
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break;
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}
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pmd_perf_end_iteration(s, rx_packets, tx_packets,
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pmd_perf_end_iteration(s, rx_packets, tx_packets, time_slept,
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pmd_perf_metrics_enabled(pmd));
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}
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ovs_mutex_unlock(&pmd->perf_stats.stats_mutex);
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@ -9909,7 +9961,7 @@ dp_netdev_pmd_try_optimize(struct dp_netdev_pmd_thread *pmd,
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struct polled_queue *poll_list, int poll_cnt)
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{
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struct dpcls *cls;
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uint64_t tot_idle = 0, tot_proc = 0;
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uint64_t tot_idle = 0, tot_proc = 0, tot_sleep = 0;
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unsigned int pmd_load = 0;
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if (pmd->ctx.now > pmd->next_cycle_store) {
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@ -9926,10 +9978,13 @@ dp_netdev_pmd_try_optimize(struct dp_netdev_pmd_thread *pmd,
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pmd->prev_stats[PMD_CYCLES_ITER_IDLE];
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tot_proc = pmd->perf_stats.counters.n[PMD_CYCLES_ITER_BUSY] -
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pmd->prev_stats[PMD_CYCLES_ITER_BUSY];
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tot_sleep = pmd->perf_stats.counters.n[PMD_CYCLES_SLEEP] -
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pmd->prev_stats[PMD_CYCLES_SLEEP];
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if (pmd_alb->is_enabled && !pmd->isolated) {
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if (tot_proc) {
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pmd_load = ((tot_proc * 100) / (tot_idle + tot_proc));
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pmd_load = ((tot_proc * 100) /
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(tot_idle + tot_proc + tot_sleep));
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}
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atomic_read_relaxed(&pmd_alb->rebalance_load_thresh,
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@ -9946,6 +10001,8 @@ dp_netdev_pmd_try_optimize(struct dp_netdev_pmd_thread *pmd,
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pmd->perf_stats.counters.n[PMD_CYCLES_ITER_IDLE];
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pmd->prev_stats[PMD_CYCLES_ITER_BUSY] =
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pmd->perf_stats.counters.n[PMD_CYCLES_ITER_BUSY];
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pmd->prev_stats[PMD_CYCLES_SLEEP] =
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pmd->perf_stats.counters.n[PMD_CYCLES_SLEEP];
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/* Get the cycles that were used to process each queue and store. */
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for (unsigned i = 0; i < poll_cnt; i++) {
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46
tests/pmd.at
46
tests/pmd.at
@ -1254,3 +1254,49 @@ ovs-appctl: ovs-vswitchd: server returned an error
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OVS_VSWITCHD_STOP
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AT_CLEANUP
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dnl Check default state
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AT_SETUP([PMD - pmd sleep])
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OVS_VSWITCHD_START
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dnl Check default
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OVS_WAIT_UNTIL([tail ovs-vswitchd.log | grep "PMD max sleep request is 0 usecs."])
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OVS_WAIT_UNTIL([tail ovs-vswitchd.log | grep "PMD load based sleeps are disabled."])
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dnl Check low value max sleep
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="1"])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 10 usecs."])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are enabled."])
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dnl Check high value max sleep
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="10000"])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 10000 usecs."])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are enabled."])
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dnl Check setting max sleep to zero
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="0"])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 0 usecs."])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are disabled."])
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dnl Check above high value max sleep
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="10001"])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 10000 usecs."])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are enabled."])
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dnl Check rounding
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="490"])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 490 usecs."])
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OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are enabled."])
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dnl Check rounding
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get_log_next_line_num
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AT_CHECK([ovs-vsctl set open_vswitch . other_config:pmd-maxsleep="491"])
|
||||
OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD max sleep request is 500 usecs."])
|
||||
OVS_WAIT_UNTIL([tail -n +$LINENUM ovs-vswitchd.log | grep "PMD load based sleeps are enabled."])
|
||||
|
||||
OVS_VSWITCHD_STOP
|
||||
AT_CLEANUP
|
||||
|
||||
@ -788,6 +788,32 @@
|
||||
The default value is <code>25%</code>.
|
||||
</p>
|
||||
</column>
|
||||
<column name="other_config" key="pmd-maxsleep"
|
||||
type='{"type": "integer",
|
||||
"minInteger": 0, "maxInteger": 10000}'>
|
||||
<p>
|
||||
Specifies the maximum sleep time that will be requested in
|
||||
microseconds per iteration for a PMD thread which has received zero
|
||||
or a small amount of packets from the Rx queues it is polling.
|
||||
</p>
|
||||
<p>
|
||||
The actual sleep time requested is based on the load
|
||||
of the Rx queues that the PMD polls and may be less than
|
||||
the maximum value.
|
||||
</p>
|
||||
<p>
|
||||
The default value is <code>0 microseconds</code>, which means
|
||||
that the PMD will not sleep regardless of the load from the
|
||||
Rx queues that it polls.
|
||||
</p>
|
||||
<p>
|
||||
To avoid requesting very small sleeps (e.g. less than 10 us) the
|
||||
value will be rounded up to the nearest 10 us.
|
||||
</p>
|
||||
<p>
|
||||
The maximum value is <code>10000 microseconds</code>.
|
||||
</p>
|
||||
</column>
|
||||
<column name="other_config" key="userspace-tso-enable"
|
||||
type='{"type": "boolean"}'>
|
||||
<p>
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user