contrib/timer-wheel: import linux kernel timer-wheel

This patch imports timer-wheel[1] algorithm from the linux
kernel (~/kernel/time/timer.c) with some modifications.

Timer-wheel is an efficent way to track millions of timers for
expiry. This is a variant of the simple but RAM heavy approach
of having a list (timer bucket) for every future second.
Timer-wheel categorizes every future second into a logarithmic
array of arrays. This is done by splitting the 32 bit "timeout"
value into fixed "sliced" bits, thereby each category has a
fixed size array to which buckets are assigned.

A classic split would be 8+6+6+6 (used in this patch) which
results in 256+64+64+64 == 512 buckets. Therefore, the entire
32 bit futuristic timeouts have been mapped into 512 buckets.

[
   NOTE:
     There are other possible splits, such as "8+8+8+8", but
     this patch sticks to the widely used and tested default.
]

Therfore, the first category "holds" timers whose expiry range
is between 1..256, the next cateogry holds 257..16384, third
category 16385..1048576 and so on. When timers are added,
unless it's in the first category, timers with different
timeouts could end up in the same bucket. This means that the
timers are "partially sorted" -- sorted in their highest bits.

The expiry code walks the first array of buckets and exprires
any pending timers (1..256). Next, at time value 257, timers
in the first bucket of the second array is "cascaded" onto
the first category and timers are placed into respective
buckets according to the thier timeout values. Cascading
"brings down" the timers timeout to the coorect bucket
of their respective category. Therefore, timers are sorted
by their highest bits of the timeout value and then by the
lower bits too.

[1] https://lwn.net/Articles/152436/

Change-Id: I1219abf69290961ae9a3d483e11c107c5f49c4e3
BUG: 1170075
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/9707
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 71 insertions, 0 deletions

diff --git a/contrib/timer-wheel/timer-wheel.h b/contrib/timer-wheel/timer-wheel.h
new file mode 100644
index 00000000000..74b8dfdff5e
--- /dev/null
+++ b/contrib/timer-wheel/timer-wheel.h
@@ -0,0 +1,71 @@
+/*
+  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 of the License, or
+  (at your option) any later version.
+
+  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, write to the Free Software Foundation, Inc.,
+  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef __TIMER_WHEEL_H
+#define __TIMER_WHEEL_H
+
+#include <pthread.h>
+
+#include "list.h"
+
+#define TVR_BITS  8
+#define TVN_BITS  6
+#define TVR_SIZE  (1 << TVR_BITS)
+#define TVN_SIZE  (1 << TVN_BITS)
+#define TVR_MASK  (TVR_SIZE - 1)
+#define TVN_MASK  (TVN_SIZE - 1)
+
+#define BITS_PER_LONG  64
+
+struct tvec {
+        struct list_head vec[TVN_SIZE];
+};
+
+struct tvec_root {
+        struct list_head vec[TVR_SIZE];
+};
+
+struct tvec_base {
+        pthread_spinlock_t lock;      /* base lock */
+
+        pthread_t runner;             /* run_timer() */
+
+        unsigned long timer_sec;      /* time counter */
+
+        struct tvec_root tv1;
+        struct tvec tv2;
+        struct tvec tv3;
+        struct tvec tv4;
+        struct tvec tv5;
+};
+
+struct gf_tw_timer_list {
+        void *data;
+        unsigned long expires;
+
+        /** callback routine */
+        void (*function)(struct gf_tw_timer_list *, void *, unsigned long);
+
+        struct list_head entry;
+};
+
+/** The API! */
+struct tvec_base *gf_tw_init_timers ();
+int gf_tw_cleanup_timers (struct tvec_base *);
+void gf_tw_add_timer (struct tvec_base *, struct gf_tw_timer_list *);
+void gf_tw_del_timer (struct gf_tw_timer_list *);
+
+#endif