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dpif-netdev: Refactor cycle counting
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Simplify the historically grown TSC cycle counting in PMD threads.
Cycles are currently counted for the following purposes:

1. Measure PMD ustilization

PMD utilization is defined as ratio of cycles spent in busy iterations
(at least one packet received or sent) over the total number of cycles.

This is already done in pmd_perf_start_iteration() and
pmd_perf_end_iteration() based on a TSC timestamp saved in current
iteration at start_iteration() and the actual TSC at end_iteration().
No dependency on intermediate cycle accounting.

2. Measure the processing load per RX queue

This comprises cycles spend on polling and processing packets received
from the rx queue and the cycles spent on delayed sending of these packets
to tx queues (with time-based batching).

The previous scheme using cycles_count_start(), cycles_count_intermediate()
and cycles-count_end() originally introduced to simplify cycle counting
and saving calls to rte_get_tsc_cycles() was rather obscuring things.

Replace by a nestable cycle_timer with with start and stop functions to
embrace a code segment to be timed. The timed code may contain arbitrary
nested cycle_timers. The duration of nested timers is excluded from the
outer timer.

The caller must ensure that each call to cycle_timer_start() is
followed by a call to cycle_timer_end(). Failure to do so will lead to
assertion failure or a memory leak.

The new cycle_timer is used to measure the processing cycles per rx queue.
This is not yet strictly necessary but will be made use of in a subsequent
commit.

All cycle count functions and data are relocated to module
dpif-netdev-perf.

Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Billy O'Mahony <billy.o.mahony@intel.com>
Signed-off: Ian Stokes <ian.stokes@intel.com>
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@JanScheurich @istokes
JanScheurich authored and istokes committed Jan 17, 2018
1 parent 82a48ea commit a19896a
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Showing 2 changed files with 134 additions and 94 deletions.
110 changes: 101 additions & 9 deletions lib/dpif-netdev-perf.h
View file
Expand Up @@ -23,6 +23,11 @@
#include <string.h>
#include <math.h>

#ifdef DPDK_NETDEV
#include <rte_config.h>
#include <rte_cycles.h>
#endif

#include "openvswitch/vlog.h"
#include "ovs-atomic.h"
#include "timeval.h"
Expand Down Expand Up @@ -59,10 +64,6 @@ enum pmd_stat_type {
* recirculation. */
PMD_STAT_SENT_PKTS, /* Packets that have been sent. */
PMD_STAT_SENT_BATCHES, /* Number of batches sent. */
PMD_CYCLES_POLL_IDLE, /* Cycles spent unsuccessful polling. */
PMD_CYCLES_POLL_BUSY, /* Cycles spent successfully polling and
* processing polled packets. */
PMD_CYCLES_OVERHEAD, /* Cycles spent for other tasks. */
PMD_CYCLES_ITER_IDLE, /* Cycles spent in idle iterations. */
PMD_CYCLES_ITER_BUSY, /* Cycles spent in busy iterations. */
PMD_N_STATS
Expand All @@ -85,11 +86,95 @@ struct pmd_counters {

struct pmd_perf_stats {
/* Start of the current PMD iteration in TSC cycles.*/
uint64_t start_it_tsc;
/* Latest TSC time stamp taken in PMD. */
uint64_t last_tsc;
/* If non-NULL, outermost cycle timer currently running in PMD. */
struct cycle_timer *cur_timer;
/* Set of PMD counters with their zero offsets. */
struct pmd_counters counters;
};

/* Support for accurate timing of PMD execution on TSC clock cycle level.
* These functions are intended to be invoked in the context of pmd threads. */

/* Read the TSC cycle register and cache it. Any function not requiring clock
* cycle accuracy should read the cached value using cycles_counter_get() to
* avoid the overhead of reading the TSC register. */

static inline uint64_t
cycles_counter_update(struct pmd_perf_stats *s)
{
#ifdef DPDK_NETDEV
return s->last_tsc = rte_get_tsc_cycles();
#else
return s->last_tsc = 0;
#endif
}

static inline uint64_t
cycles_counter_get(struct pmd_perf_stats *s)
{
return s->last_tsc;
}

/* A nestable timer for measuring execution time in TSC cycles.
*
* Usage:
* struct cycle_timer timer;
*
* cycle_timer_start(pmd, &timer);
* <Timed execution>
* uint64_t cycles = cycle_timer_stop(pmd, &timer);
*
* The caller must guarantee that a call to cycle_timer_start() is always
* paired with a call to cycle_stimer_stop().
*
* Is is possible to have nested cycles timers within the timed code. The
* execution time measured by the nested timers is excluded from the time
* measured by the embracing timer.
*/

struct cycle_timer {
uint64_t start;
uint64_t suspended;
struct cycle_timer *interrupted;
};

static inline void
cycle_timer_start(struct pmd_perf_stats *s,
struct cycle_timer *timer)
{
struct cycle_timer *cur_timer = s->cur_timer;
uint64_t now = cycles_counter_update(s);

if (cur_timer) {
cur_timer->suspended = now;
}
timer->interrupted = cur_timer;
timer->start = now;
timer->suspended = 0;
s->cur_timer = timer;
}

static inline uint64_t
cycle_timer_stop(struct pmd_perf_stats *s,
struct cycle_timer *timer)
{
/* Assert that this is the current cycle timer. */
ovs_assert(s->cur_timer == timer);
uint64_t now = cycles_counter_update(s);
struct cycle_timer *intr_timer = timer->interrupted;

if (intr_timer) {
/* Adjust the start offset by the suspended cycles. */
intr_timer->start += now - intr_timer->suspended;
}
/* Restore suspended timer, if any. */
s->cur_timer = intr_timer;
return now - timer->start;
}

void pmd_perf_stats_init(struct pmd_perf_stats *s);
void pmd_perf_stats_clear(struct pmd_perf_stats *s);
void pmd_perf_read_counters(struct pmd_perf_stats *s,
Expand All @@ -115,16 +200,23 @@ pmd_perf_update_counter(struct pmd_perf_stats *s,
}

static inline void
pmd_perf_start_iteration(struct pmd_perf_stats *s, uint64_t now_tsc)
pmd_perf_start_iteration(struct pmd_perf_stats *s)
{
s->last_tsc = now_tsc;
if (OVS_LIKELY(s->last_tsc)) {
/* We assume here that last_tsc was updated immediately prior at
* the end of the previous iteration, or just before the first
* iteration. */
s->start_it_tsc = s->last_tsc;
} else {
/* In case last_tsc has never been set before. */
s->start_it_tsc = cycles_counter_update(s);
}
}

static inline void
pmd_perf_end_iteration(struct pmd_perf_stats *s, uint64_t now_tsc,
int rx_packets)
pmd_perf_end_iteration(struct pmd_perf_stats *s, int rx_packets)
{
uint64_t cycles = now_tsc - s->last_tsc;
uint64_t cycles = cycles_counter_update(s) - s->start_it_tsc;

if (rx_packets > 0) {
pmd_perf_update_counter(s, PMD_CYCLES_ITER_BUSY, cycles);
Expand Down
118 changes: 33 additions & 85 deletions lib/dpif-netdev.c
View file
Expand Up @@ -32,10 +32,6 @@
#include <sys/stat.h>
#include <unistd.h>

#ifdef DPDK_NETDEV
#include <rte_cycles.h>
#endif

#include "bitmap.h"
#include "cmap.h"
#include "conntrack.h"
Expand Down Expand Up @@ -509,8 +505,6 @@ struct tx_port {
struct dp_netdev_pmd_thread_ctx {
/* Latest measured time. See 'pmd_thread_ctx_time_update()'. */
long long now;
/* Used to count cycles. See 'cycles_count_end()' */
unsigned long long last_cycles;
};

/* PMD: Poll modes drivers. PMD accesses devices via polling to eliminate
Expand Down Expand Up @@ -3111,64 +3105,20 @@ dp_netdev_actions_free(struct dp_netdev_actions *actions)
free(actions);
}

static inline unsigned long long
cycles_counter(void)
{
#ifdef DPDK_NETDEV
return rte_get_tsc_cycles();
#else
return 0;
#endif
}

/* Fake mutex to make sure that the calls to cycles_count_* are balanced */
extern struct ovs_mutex cycles_counter_fake_mutex;

/* Start counting cycles. Must be followed by 'cycles_count_end()' */
static inline void
cycles_count_start(struct dp_netdev_pmd_thread *pmd)
OVS_ACQUIRES(&cycles_counter_fake_mutex)
OVS_NO_THREAD_SAFETY_ANALYSIS
{
pmd->ctx.last_cycles = cycles_counter();
}

/* Stop counting cycles and add them to the counter 'type' */
static inline void
cycles_count_end(struct dp_netdev_pmd_thread *pmd,
enum pmd_stat_type type)
OVS_RELEASES(&cycles_counter_fake_mutex)
OVS_NO_THREAD_SAFETY_ANALYSIS
{
unsigned long long interval = cycles_counter() - pmd->ctx.last_cycles;

pmd_perf_update_counter(&pmd->perf_stats, type, interval);
}

/* Calculate the intermediate cycle result and add to the counter 'type' */
static inline void
cycles_count_intermediate(struct dp_netdev_pmd_thread *pmd,
struct dp_netdev_rxq *rxq,
enum pmd_stat_type type)
OVS_NO_THREAD_SAFETY_ANALYSIS
static void
dp_netdev_rxq_set_cycles(struct dp_netdev_rxq *rx,
enum rxq_cycles_counter_type type,
unsigned long long cycles)
{
unsigned long long new_cycles = cycles_counter();
unsigned long long interval = new_cycles - pmd->ctx.last_cycles;
pmd->ctx.last_cycles = new_cycles;

pmd_perf_update_counter(&pmd->perf_stats, type, interval);
if (rxq && (type == PMD_CYCLES_POLL_BUSY)) {
/* Add to the amount of current processing cycles. */
non_atomic_ullong_add(&rxq->cycles[RXQ_CYCLES_PROC_CURR], interval);
}
atomic_store_relaxed(&rx->cycles[type], cycles);
}

static void
dp_netdev_rxq_set_cycles(struct dp_netdev_rxq *rx,
dp_netdev_rxq_add_cycles(struct dp_netdev_rxq *rx,
enum rxq_cycles_counter_type type,
unsigned long long cycles)
{
atomic_store_relaxed(&rx->cycles[type], cycles);
non_atomic_ullong_add(&rx->cycles[type], cycles);
}

static uint64_t
Expand Down Expand Up @@ -3234,27 +3184,40 @@ dp_netdev_pmd_flush_output_packets(struct dp_netdev_pmd_thread *pmd)

static int
dp_netdev_process_rxq_port(struct dp_netdev_pmd_thread *pmd,
struct netdev_rxq *rx,
struct dp_netdev_rxq *rxq,
odp_port_t port_no)
{
struct dp_packet_batch batch;
struct cycle_timer timer;
int error;
int batch_cnt = 0;

/* Measure duration for polling and processing rx burst. */
cycle_timer_start(&pmd->perf_stats, &timer);
dp_packet_batch_init(&batch);
error = netdev_rxq_recv(rx, &batch);
error = netdev_rxq_recv(rxq->rx, &batch);
if (!error) {
/* At least one packet received. */
*recirc_depth_get() = 0;
pmd_thread_ctx_time_update(pmd);

batch_cnt = batch.count;
dp_netdev_input(pmd, &batch, port_no);
dp_netdev_pmd_flush_output_packets(pmd);
} else if (error != EAGAIN && error != EOPNOTSUPP) {
static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);

VLOG_ERR_RL(&rl, "error receiving data from %s: %s",
netdev_rxq_get_name(rx), ovs_strerror(error));
/* Assign processing cycles to rx queue. */
uint64_t cycles = cycle_timer_stop(&pmd->perf_stats, &timer);
dp_netdev_rxq_add_cycles(rxq, RXQ_CYCLES_PROC_CURR, cycles);

} else {
/* Discard cycles. */
cycle_timer_stop(&pmd->perf_stats, &timer);
if (error != EAGAIN && error != EOPNOTSUPP) {
static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);

VLOG_ERR_RL(&rl, "error receiving data from %s: %s",
netdev_rxq_get_name(rxq->rx), ovs_strerror(error));
}
}

return batch_cnt;
Expand Down Expand Up @@ -3880,30 +3843,22 @@ dpif_netdev_run(struct dpif *dpif)
struct dp_netdev *dp = get_dp_netdev(dpif);
struct dp_netdev_pmd_thread *non_pmd;
uint64_t new_tnl_seq;
int process_packets = 0;

ovs_mutex_lock(&dp->port_mutex);
non_pmd = dp_netdev_get_pmd(dp, NON_PMD_CORE_ID);
if (non_pmd) {
ovs_mutex_lock(&dp->non_pmd_mutex);
cycles_count_start(non_pmd);
HMAP_FOR_EACH (port, node, &dp->ports) {
if (!netdev_is_pmd(port->netdev)) {
int i;

for (i = 0; i < port->n_rxq; i++) {
process_packets =
dp_netdev_process_rxq_port(non_pmd,
port->rxqs[i].rx,
port->port_no);
cycles_count_intermediate(non_pmd, NULL,
process_packets
? PMD_CYCLES_POLL_BUSY
: PMD_CYCLES_POLL_IDLE);
dp_netdev_process_rxq_port(non_pmd,
&port->rxqs[i],
port->port_no);
}
}
}
cycles_count_end(non_pmd, PMD_CYCLES_POLL_IDLE);
pmd_thread_ctx_time_update(non_pmd);
dpif_netdev_xps_revalidate_pmd(non_pmd, false);
ovs_mutex_unlock(&dp->non_pmd_mutex);
Expand Down Expand Up @@ -4082,18 +4037,14 @@ pmd_thread_main(void *f_)
lc = UINT_MAX;
}

cycles_count_start(pmd);
cycles_counter_update(s);
for (;;) {
uint64_t iter_packets = 0;
pmd_perf_start_iteration(s, pmd->ctx.last_cycles);
pmd_perf_start_iteration(s);
for (i = 0; i < poll_cnt; i++) {
process_packets =
dp_netdev_process_rxq_port(pmd, poll_list[i].rxq->rx,
dp_netdev_process_rxq_port(pmd, poll_list[i].rxq,
poll_list[i].port_no);
cycles_count_intermediate(pmd, poll_list[i].rxq,
process_packets
? PMD_CYCLES_POLL_BUSY
: PMD_CYCLES_POLL_IDLE);
iter_packets += process_packets;
}

Expand All @@ -4115,13 +4066,10 @@ pmd_thread_main(void *f_)
if (reload) {
break;
}
cycles_count_intermediate(pmd, NULL, PMD_CYCLES_OVERHEAD);
}
pmd_perf_end_iteration(s, pmd->ctx.last_cycles, iter_packets);
pmd_perf_end_iteration(s, iter_packets);
}

cycles_count_end(pmd, PMD_CYCLES_OVERHEAD);

poll_cnt = pmd_load_queues_and_ports(pmd, &poll_list);
exiting = latch_is_set(&pmd->exit_latch);
/* Signal here to make sure the pmd finishes
Expand Down

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