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Commit
237588ee
authored
Apr 30, 2019
by
FritzFlorian
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Add basic backoff to stealing mechanism.
parent
25d18c11
Pipeline
#1161
passed with stages
in 3 minutes 40 seconds
Changes
3
Pipelines
1
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3 changed files
with
18 additions
and
64 deletions
+18
-64
lib/pls/include/pls/internal/base/backoff.h
+9
-5
lib/pls/include/pls/internal/data_structures/work_stealing_deque.h
+3
-59
lib/pls/src/internal/scheduling/abstract_task.cpp
+6
-0
No files found.
lib/pls/include/pls/internal/base/backoff.h
View file @
237588ee
...
...
@@ -14,8 +14,10 @@ namespace internal {
namespace
base
{
class
backoff
{
const
unsigned
long
INITIAL_SPIN_ITERS
=
2u
<<
2u
;
const
unsigned
long
MAX_SPIN_ITERS
=
2u
<<
6u
;
const
unsigned
long
INITIAL_SPIN_ITERS
=
2u
<<
4u
;
const
unsigned
long
MAX_SPIN_ITERS
=
2u
<<
8u
;
const
unsigned
long
MAX_ITERS
=
2u
<<
10u
;
const
unsigned
long
YELD_ITERS
=
2u
<<
10u
;
unsigned
long
current_
=
INITIAL_SPIN_ITERS
;
std
::
minstd_rand
random_
;
...
...
@@ -32,10 +34,12 @@ class backoff {
PROFILE_LOCK
(
"Backoff"
)
spin
(
random_
()
%
std
::
min
(
current_
,
MAX_SPIN_ITERS
));
current_
=
current_
*
2
;
if
(
current_
>
MAX_SPIN_ITERS
)
{
current_
=
MAX_SPIN_ITERS
;
if
(
current_
>=
YELD_ITERS
)
{
PROFILE_LOCK
(
"Yield"
)
this_thread
::
yield
()
;
}
current_
=
std
::
min
(
current_
*
2
,
MAX_ITERS
);
}
void
reset
()
{
...
...
lib/pls/include/pls/internal/data_structures/work_stealing_deque.h
View file @
237588ee
...
...
@@ -12,8 +12,6 @@
#include "aligned_stack.h"
//#define LOCK_FREE_DEBUG_PRINT
namespace
pls
{
namespace
internal
{
namespace
data_structures
{
...
...
@@ -87,10 +85,10 @@ class work_stealing_deque {
using
state
=
aligned_stack
::
state
;
explicit
work_stealing_deque
(
aligned_stack
*
stack
)
:
stack_
{
stack
},
base_pointer_
{
0
},
head_
{
0
},
tail_
{
0
},
previous_tail_
{
0
},
base_pointer_
{
0
}
{
previous_tail_
{
0
}
{
reset_base_pointer
();
}
work_stealing_deque
(
const
work_stealing_deque
&
other
)
:
stack_
{
other
.
stack_
},
...
...
@@ -128,9 +126,6 @@ class work_stealing_deque {
template
<
typename
T
>
Item
*
push_tail
(
const
T
&
new_item
)
{
cas_integer
local_tail
=
tail_
;
cas_integer
local_head
=
head_
;
PLS_ASSERT
((
local_tail
>=
get_offset
(
local_head
)),
"Tail MUST be in front of head!"
)
auto
new_pair
=
allocate_item
(
new_item
);
// Prepare current tail to point to correct next items
...
...
@@ -143,13 +138,6 @@ class work_stealing_deque {
// Linearization point, item appears after this write
cas_integer
new_tail
=
current_stack_offset
();
tail_
=
new_tail
;
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Pushed Tail "
<<
local_tail
<<
"->"
<<
new_tail
<<
std
::
endl
;
}
#endif
return
&
(
new_pair
->
second
);
}
...
...
@@ -172,13 +160,6 @@ class work_stealing_deque {
local_head
=
head_
;
// Linearization point, outside knows list is empty
if
(
get_offset
(
local_head
)
<
new_tail
)
{
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Poped Tail (distance) "
<<
local_tail
<<
"->"
<<
new_tail
<<
std
::
endl
;
}
#endif
return
previous_tail_item
->
data
<
Item
>
();
// Success, enough distance to other threads
}
...
...
@@ -186,26 +167,10 @@ class work_stealing_deque {
cas_integer
new_head
=
set_stamp
(
new_tail
,
get_stamp
(
local_head
)
+
1
);
// Try competing with consumers by updating the head's stamp value
if
(
head_
.
compare_exchange_strong
(
local_head
,
new_head
))
{
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Poped Tail (won competition 1) "
<<
local_tail
<<
"->"
<<
new_tail
<<
std
::
endl
;
}
#endif
return
previous_tail_item
->
data
<
Item
>
();
// SUCCESS, we won the competition with other threads
}
}
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"FAILED to pop tail (lost competition) "
<<
get_offset
(
local_head
)
<<
"; "
<<
local_tail
<<
"->"
<<
new_tail
<<
std
::
endl
;
}
#endif
// Some other thread either won the competition or it already set the head further than we are
// before we even tried to compete with it.
// Reset the queue into an empty state => head_ = tail_
...
...
@@ -236,22 +201,9 @@ class work_stealing_deque {
// 3) owning thread removed tail, we lose to this
cas_integer
new_head
=
set_stamp
(
next_item_offset
,
get_stamp
(
local_head
)
+
1
);
if
(
head_
.
compare_exchange_strong
(
local_head
,
new_head
))
{
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Popped Head "
<<
get_offset
(
local_head
)
<<
"->"
<<
next_item_offset
<<
std
::
endl
;
}
#endif
return
head_data_item
;
// SUCCESS, we won the competition
}
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Failed to pop head "
<<
get_offset
(
local_head
)
<<
"->"
<<
next_item_offset
<<
std
::
endl
;
}
#endif
return
nullptr
;
// EMPTY, we lost the competition
}
...
...
@@ -270,14 +222,6 @@ class work_stealing_deque {
head_
=
set_stamp
(
item_offset
,
get_stamp
(
local_head
)
+
1
);
}
}
#ifdef LOCK_FREE_DEBUG_PRINT
{
std
::
lock_guard
<
base
::
spin_lock
>
lock
{
lock_
};
std
::
cout
<<
base
::
this_thread
::
state
<
scheduling
::
thread_state
>
()
->
id_
<<
" - "
<<
"Release Memory "
<<
item_offset
<<
std
::
endl
;
}
#endif
}
void
release_memory_until
(
Item
*
item
)
{
...
...
lib/pls/src/internal/scheduling/abstract_task.cpp
View file @
237588ee
#include <pls/internal/base/backoff.h>
#include "pls/internal/helpers/profiler.h"
#include "pls/internal/scheduling/thread_state.h"
...
...
@@ -9,6 +10,8 @@ namespace internal {
namespace
scheduling
{
bool
abstract_task
::
steal_work
()
{
thread_local
static
base
::
backoff
backoff
{};
PROFILE_STEALING
(
"abstract_task::steal_work"
)
const
auto
my_state
=
base
::
this_thread
::
state
<
thread_state
>
();
const
auto
my_scheduler
=
my_state
->
scheduler_
;
...
...
@@ -44,6 +47,7 @@ bool abstract_task::steal_work() {
if
(
internal_stealing
(
current_task
))
{
// internal steal was a success, hand it back to the internal scheduler
target_state
->
lock_
.
reader_unlock
();
backoff
.
reset
();
return
true
;
}
...
...
@@ -61,6 +65,7 @@ bool abstract_task::steal_work() {
auto
lock
=
&
target_state
->
lock_
;
if
(
current_task
->
split_task
(
lock
))
{
// top level steal was a success (we did a top level task steal)
backoff
.
reset
();
return
false
;
}
...
...
@@ -71,6 +76,7 @@ bool abstract_task::steal_work() {
}
// internal steal was no success
backoff
.
do_backoff
();
return
false
;
}
...
...
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