throttle: Add a new throttling API implementing continuous leaky bucket.

Implement the continuous leaky bucket algorithm devised on IRC as a separate
module.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 396 insertions, 0 deletions

diff --git a/util/throttle.c b/util/throttle.c
new file mode 100644
index 0000000000..02e6f15587
--- /dev/null
+++ b/util/throttle.c
@@ -0,0 +1,396 @@
+/*
+ * QEMU throttling infrastructure
+ *
+ * Copyright (C) Nodalink, SARL. 2013
+ *
+ * Author:
+ *   Benoît Canet <benoit.canet@irqsave.net>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 or
+ * (at your option) version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "qemu/throttle.h"
+#include "qemu/timer.h"
+
+/* This function make a bucket leak
+ *
+ * @bkt:   the bucket to make leak
+ * @delta_ns: the time delta
+ */
+void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta_ns)
+{
+    double leak;
+
+    /* compute how much to leak */
+    leak = (bkt->avg * (double) delta_ns) / NANOSECONDS_PER_SECOND;
+
+    /* make the bucket leak */
+    bkt->level = MAX(bkt->level - leak, 0);
+}
+
+/* Calculate the time delta since last leak and make proportionals leaks
+ *
+ * @now:      the current timestamp in ns
+ */
+static void throttle_do_leak(ThrottleState *ts, int64_t now)
+{
+    /* compute the time elapsed since the last leak */
+    int64_t delta_ns = now - ts->previous_leak;
+    int i;
+
+    ts->previous_leak = now;
+
+    if (delta_ns <= 0) {
+        return;
+    }
+
+    /* make each bucket leak */
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        throttle_leak_bucket(&ts->cfg.buckets[i], delta_ns);
+    }
+}
+
+/* do the real job of computing the time to wait
+ *
+ * @limit: the throttling limit
+ * @extra: the number of operation to delay
+ * @ret:   the time to wait in ns
+ */
+static int64_t throttle_do_compute_wait(double limit, double extra)
+{
+    double wait = extra * NANOSECONDS_PER_SECOND;
+    wait /= limit;
+    return wait;
+}
+
+/* This function compute the wait time in ns that a leaky bucket should trigger
+ *
+ * @bkt: the leaky bucket we operate on
+ * @ret: the resulting wait time in ns or 0 if the operation can go through
+ */
+int64_t throttle_compute_wait(LeakyBucket *bkt)
+{
+    double extra; /* the number of extra units blocking the io */
+
+    if (!bkt->avg) {
+        return 0;
+    }
+
+    extra = bkt->level - bkt->max;
+
+    if (extra <= 0) {
+        return 0;
+    }
+
+    return throttle_do_compute_wait(bkt->avg, extra);
+}
+
+/* This function compute the time that must be waited while this IO
+ *
+ * @is_write:   true if the current IO is a write, false if it's a read
+ * @ret:        time to wait
+ */
+static int64_t throttle_compute_wait_for(ThrottleState *ts,
+                                         bool is_write)
+{
+    BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
+                                   THROTTLE_OPS_TOTAL,
+                                   THROTTLE_BPS_READ,
+                                   THROTTLE_OPS_READ},
+                                  {THROTTLE_BPS_TOTAL,
+                                   THROTTLE_OPS_TOTAL,
+                                   THROTTLE_BPS_WRITE,
+                                   THROTTLE_OPS_WRITE}, };
+    int64_t wait, max_wait = 0;
+    int i;
+
+    for (i = 0; i < 4; i++) {
+        BucketType index = to_check[is_write][i];
+        wait = throttle_compute_wait(&ts->cfg.buckets[index]);
+        if (wait > max_wait) {
+            max_wait = wait;
+        }
+    }
+
+    return max_wait;
+}
+
+/* compute the timer for this type of operation
+ *
+ * @is_write:   the type of operation
+ * @now:        the current clock timestamp
+ * @next_timestamp: the resulting timer
+ * @ret:        true if a timer must be set
+ */
+bool throttle_compute_timer(ThrottleState *ts,
+                            bool is_write,
+                            int64_t now,
+                            int64_t *next_timestamp)
+{
+    int64_t wait;
+
+    /* leak proportionally to the time elapsed */
+    throttle_do_leak(ts, now);
+
+    /* compute the wait time if any */
+    wait = throttle_compute_wait_for(ts, is_write);
+
+    /* if the code must wait compute when the next timer should fire */
+    if (wait) {
+        *next_timestamp = now + wait;
+        return true;
+    }
+
+    /* else no need to wait at all */
+    *next_timestamp = now;
+    return false;
+}
+
+/* To be called first on the ThrottleState */
+void throttle_init(ThrottleState *ts,
+                   QEMUClockType clock_type,
+                   QEMUTimerCB *read_timer_cb,
+                   QEMUTimerCB *write_timer_cb,
+                   void *timer_opaque)
+{
+    memset(ts, 0, sizeof(ThrottleState));
+
+    ts->clock_type = clock_type;
+    ts->timers[0] = timer_new_ns(clock_type, read_timer_cb, timer_opaque);
+    ts->timers[1] = timer_new_ns(clock_type, write_timer_cb, timer_opaque);
+}
+
+/* destroy a timer */
+static void throttle_timer_destroy(QEMUTimer **timer)
+{
+    assert(*timer != NULL);
+
+    timer_del(*timer);
+    timer_free(*timer);
+    *timer = NULL;
+}
+
+/* To be called last on the ThrottleState */
+void throttle_destroy(ThrottleState *ts)
+{
+    int i;
+
+    for (i = 0; i < 2; i++) {
+        throttle_timer_destroy(&ts->timers[i]);
+    }
+}
+
+/* is any throttling timer configured */
+bool throttle_have_timer(ThrottleState *ts)
+{
+    if (ts->timers[0]) {
+        return true;
+    }
+
+    return false;
+}
+
+/* Does any throttling must be done
+ *
+ * @cfg: the throttling configuration to inspect
+ * @ret: true if throttling must be done else false
+ */
+bool throttle_enabled(ThrottleConfig *cfg)
+{
+    int i;
+
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        if (cfg->buckets[i].avg > 0) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/* return true if any two throttling parameters conflicts
+ *
+ * @cfg: the throttling configuration to inspect
+ * @ret: true if any conflict detected else false
+ */
+bool throttle_conflicting(ThrottleConfig *cfg)
+{
+    bool bps_flag, ops_flag;
+    bool bps_max_flag, ops_max_flag;
+
+    bps_flag = cfg->buckets[THROTTLE_BPS_TOTAL].avg &&
+               (cfg->buckets[THROTTLE_BPS_READ].avg ||
+                cfg->buckets[THROTTLE_BPS_WRITE].avg);
+
+    ops_flag = cfg->buckets[THROTTLE_OPS_TOTAL].avg &&
+               (cfg->buckets[THROTTLE_OPS_READ].avg ||
+                cfg->buckets[THROTTLE_OPS_WRITE].avg);
+
+    bps_max_flag = cfg->buckets[THROTTLE_BPS_TOTAL].max &&
+                  (cfg->buckets[THROTTLE_BPS_READ].max  ||
+                   cfg->buckets[THROTTLE_BPS_WRITE].max);
+
+    ops_max_flag = cfg->buckets[THROTTLE_OPS_TOTAL].max &&
+                   (cfg->buckets[THROTTLE_OPS_READ].max ||
+                   cfg->buckets[THROTTLE_OPS_WRITE].max);
+
+    return bps_flag || ops_flag || bps_max_flag || ops_max_flag;
+}
+
+/* check if a throttling configuration is valid
+ * @cfg: the throttling configuration to inspect
+ * @ret: true if valid else false
+ */
+bool throttle_is_valid(ThrottleConfig *cfg)
+{
+    bool invalid = false;
+    int i;
+
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        if (cfg->buckets[i].avg < 0) {
+            invalid = true;
+        }
+    }
+
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        if (cfg->buckets[i].max < 0) {
+            invalid = true;
+        }
+    }
+
+    return !invalid;
+}
+
+/* fix bucket parameters */
+static void throttle_fix_bucket(LeakyBucket *bkt)
+{
+    double min;
+
+    /* zero bucket level */
+    bkt->level = 0;
+
+    /* The following is done to cope with the Linux CFQ block scheduler
+     * which regroup reads and writes by block of 100ms in the guest.
+     * When they are two process one making reads and one making writes cfq
+     * make a pattern looking like the following:
+     * WWWWWWWWWWWRRRRRRRRRRRRRRWWWWWWWWWWWWWwRRRRRRRRRRRRRRRRR
+     * Having a max burst value of 100ms of the average will help smooth the
+     * throttling
+     */
+    min = bkt->avg / 10;
+    if (bkt->avg && !bkt->max) {
+        bkt->max = min;
+    }
+}
+
+/* take care of canceling a timer */
+static void throttle_cancel_timer(QEMUTimer *timer)
+{
+    assert(timer != NULL);
+
+    timer_del(timer);
+}
+
+/* Used to configure the throttle
+ *
+ * @ts: the throttle state we are working on
+ * @cfg: the config to set
+ */
+void throttle_config(ThrottleState *ts, ThrottleConfig *cfg)
+{
+    int i;
+
+    ts->cfg = *cfg;
+
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        throttle_fix_bucket(&ts->cfg.buckets[i]);
+    }
+
+    ts->previous_leak = qemu_clock_get_ns(ts->clock_type);
+
+    for (i = 0; i < 2; i++) {
+        throttle_cancel_timer(ts->timers[i]);
+    }
+}
+
+/* used to get config
+ *
+ * @ts:  the throttle state we are working on
+ * @cfg: the config to write
+ */
+void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
+{
+    *cfg = ts->cfg;
+}
+
+
+/* Schedule the read or write timer if needed
+ *
+ * NOTE: this function is not unit tested due to it's usage of timer_mod
+ *
+ * @is_write: the type of operation (read/write)
+ * @ret:      true if the timer has been scheduled else false
+ */
+bool throttle_schedule_timer(ThrottleState *ts, bool is_write)
+{
+    int64_t now = qemu_clock_get_ns(ts->clock_type);
+    int64_t next_timestamp;
+    bool must_wait;
+
+    must_wait = throttle_compute_timer(ts,
+                                       is_write,
+                                       now,
+                                       &next_timestamp);
+
+    /* request not throttled */
+    if (!must_wait) {
+        return false;
+    }
+
+    /* request throttled and timer pending -> do nothing */
+    if (timer_pending(ts->timers[is_write])) {
+        return true;
+    }
+
+    /* request throttled and timer not pending -> arm timer */
+    timer_mod(ts->timers[is_write], next_timestamp);
+    return true;
+}
+
+/* do the accounting for this operation
+ *
+ * @is_write: the type of operation (read/write)
+ * @size:     the size of the operation
+ */
+void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
+{
+    double units = 1.0;
+
+    /* if cfg.op_size is defined and smaller than size we compute unit count */
+    if (ts->cfg.op_size && size > ts->cfg.op_size) {
+        units = (double) size / ts->cfg.op_size;
+    }
+
+    ts->cfg.buckets[THROTTLE_BPS_TOTAL].level += size;
+    ts->cfg.buckets[THROTTLE_OPS_TOTAL].level += units;
+
+    if (is_write) {
+        ts->cfg.buckets[THROTTLE_BPS_WRITE].level += size;
+        ts->cfg.buckets[THROTTLE_OPS_WRITE].level += units;
+    } else {
+        ts->cfg.buckets[THROTTLE_BPS_READ].level += size;
+        ts->cfg.buckets[THROTTLE_OPS_READ].level += units;
+    }
+}
+