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, 110 insertions, 0 deletions

diff --git a/include/qemu/throttle.h b/include/qemu/throttle.h
new file mode 100644
index 0000000..ab29b0b
--- /dev/null
+++ b/include/qemu/throttle.h
@@ -0,0 +1,110 @@
+/*
+ * 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/>.
+ */
+
+#ifndef THROTTLE_H
+#define THROTTLE_H
+
+#include <stdint.h>
+#include "qemu-common.h"
+#include "qemu/timer.h"
+
+#define NANOSECONDS_PER_SECOND  1000000000.0
+
+typedef enum {
+    THROTTLE_BPS_TOTAL,
+    THROTTLE_BPS_READ,
+    THROTTLE_BPS_WRITE,
+    THROTTLE_OPS_TOTAL,
+    THROTTLE_OPS_READ,
+    THROTTLE_OPS_WRITE,
+    BUCKETS_COUNT,
+} BucketType;
+
+/*
+ * The max parameter of the leaky bucket throttling algorithm can be used to
+ * allow the guest to do bursts.
+ * The max value is a pool of I/O that the guest can use without being throttled
+ * at all. Throttling is triggered once this pool is empty.
+ */
+
+typedef struct LeakyBucket {
+    double  avg;              /* average goal in units per second */
+    double  max;              /* leaky bucket max burst in units */
+    double  level;            /* bucket level in units */
+} LeakyBucket;
+
+/* The following structure is used to configure a ThrottleState
+ * It contains a bit of state: the bucket field of the LeakyBucket structure.
+ * However it allows to keep the code clean and the bucket field is reset to
+ * zero at the right time.
+ */
+typedef struct ThrottleConfig {
+    LeakyBucket buckets[BUCKETS_COUNT]; /* leaky buckets */
+    uint64_t op_size;         /* size of an operation in bytes */
+} ThrottleConfig;
+
+typedef struct ThrottleState {
+    ThrottleConfig cfg;       /* configuration */
+    int64_t previous_leak;    /* timestamp of the last leak done */
+    QEMUTimer * timers[2];    /* timers used to do the throttling */
+    QEMUClockType clock_type; /* the clock used */
+} ThrottleState;
+
+/* operations on single leaky buckets */
+void throttle_leak_bucket(LeakyBucket *bkt, int64_t delta);
+
+int64_t throttle_compute_wait(LeakyBucket *bkt);
+
+/* expose timer computation function for unit tests */
+bool throttle_compute_timer(ThrottleState *ts,
+                            bool is_write,
+                            int64_t now,
+                            int64_t *next_timestamp);
+
+/* init/destroy cycle */
+void throttle_init(ThrottleState *ts,
+                   QEMUClockType clock_type,
+                   void (read_timer)(void *),
+                   void (write_timer)(void *),
+                   void *timer_opaque);
+
+void throttle_destroy(ThrottleState *ts);
+
+bool throttle_have_timer(ThrottleState *ts);
+
+/* configuration */
+bool throttle_enabled(ThrottleConfig *cfg);
+
+bool throttle_conflicting(ThrottleConfig *cfg);
+
+bool throttle_is_valid(ThrottleConfig *cfg);
+
+void throttle_config(ThrottleState *ts, ThrottleConfig *cfg);
+
+void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg);
+
+/* usage */
+bool throttle_schedule_timer(ThrottleState *ts, bool is_write);
+
+void throttle_account(ThrottleState *ts, bool is_write, uint64_t size);
+
+#endif