count "dud" sparks (expressions that were already evaluated when sparked)
[ghc.git] / rts / Sparks.c
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 2000-2008
4 *
5 * Sparking support for PARALLEL_HASKELL and THREADED_RTS versions of the RTS.
6 *
7 -------------------------------------------------------------------------*/
8
9 #include "PosixSource.h"
10 #include "Rts.h"
11
12 #include "Schedule.h"
13 #include "RtsUtils.h"
14 #include "Trace.h"
15 #include "Prelude.h"
16 #include "Sparks.h"
17
18 #if defined(THREADED_RTS)
19
20 void
21 initSparkPools( void )
22 {
23 /* walk over the capabilities, allocating a spark pool for each one */
24 nat i;
25 for (i = 0; i < n_capabilities; i++) {
26 capabilities[i].sparks = newWSDeque(RtsFlags.ParFlags.maxLocalSparks);
27 }
28 }
29
30 void
31 freeSparkPool (SparkPool *pool)
32 {
33 freeWSDeque(pool);
34 }
35
36 /* -----------------------------------------------------------------------------
37 *
38 * Turn a spark into a real thread
39 *
40 * -------------------------------------------------------------------------- */
41
42 void
43 createSparkThread (Capability *cap)
44 {
45 StgTSO *tso;
46
47 tso = createIOThread (cap, RtsFlags.GcFlags.initialStkSize,
48 (StgClosure *)runSparks_closure);
49
50 traceEventCreateSparkThread(cap, tso->id);
51
52 appendToRunQueue(cap,tso);
53 }
54
55 /* --------------------------------------------------------------------------
56 * newSpark: create a new spark, as a result of calling "par"
57 * Called directly from STG.
58 * -------------------------------------------------------------------------- */
59
60 StgInt
61 newSpark (StgRegTable *reg, StgClosure *p)
62 {
63 Capability *cap = regTableToCapability(reg);
64 SparkPool *pool = cap->sparks;
65
66 /* I am not sure whether this is the right thing to do.
67 * Maybe it is better to exploit the tag information
68 * instead of throwing it away?
69 */
70 p = UNTAG_CLOSURE(p);
71
72 if (closure_SHOULD_SPARK(p)) {
73 pushWSDeque(pool,p);
74 cap->sparks_created++;
75 } else {
76 cap->sparks_dud++;
77 }
78
79 return 1;
80 }
81
82 /* -----------------------------------------------------------------------------
83 *
84 * tryStealSpark: try to steal a spark from a Capability.
85 *
86 * Returns a valid spark, or NULL if the pool was empty, and can
87 * occasionally return NULL if there was a race with another thread
88 * stealing from the same pool. In this case, try again later.
89 *
90 -------------------------------------------------------------------------- */
91
92 StgClosure *
93 tryStealSpark (Capability *cap)
94 {
95 SparkPool *pool = cap->sparks;
96 StgClosure *stolen;
97
98 do {
99 stolen = stealWSDeque_(pool);
100 // use the no-loopy version, stealWSDeque_(), since if we get a
101 // spurious NULL here the caller may want to try stealing from
102 // other pools before trying again.
103 } while (stolen != NULL && !closure_SHOULD_SPARK(stolen));
104
105 return stolen;
106 }
107
108 /* --------------------------------------------------------------------------
109 * Remove all sparks from the spark queues which should not spark any
110 * more. Called after GC. We assume exclusive access to the structure
111 * and replace all sparks in the queue, see explanation below. At exit,
112 * the spark pool only contains sparkable closures.
113 * -------------------------------------------------------------------------- */
114
115 void
116 pruneSparkQueue (Capability *cap)
117 {
118 SparkPool *pool;
119 StgClosurePtr spark, tmp, *elements;
120 nat n, pruned_sparks; // stats only
121 StgWord botInd,oldBotInd,currInd; // indices in array (always < size)
122 const StgInfoTable *info;
123
124 n = 0;
125 pruned_sparks = 0;
126
127 pool = cap->sparks;
128
129 // it is possible that top > bottom, indicating an empty pool. We
130 // fix that here; this is only necessary because the loop below
131 // assumes it.
132 if (pool->top > pool->bottom)
133 pool->top = pool->bottom;
134
135 // Take this opportunity to reset top/bottom modulo the size of
136 // the array, to avoid overflow. This is only possible because no
137 // stealing is happening during GC.
138 pool->bottom -= pool->top & ~pool->moduloSize;
139 pool->top &= pool->moduloSize;
140 pool->topBound = pool->top;
141
142 debugTrace(DEBUG_sparks,
143 "markSparkQueue: current spark queue len=%ld; (hd=%ld; tl=%ld)",
144 sparkPoolSize(pool), pool->bottom, pool->top);
145
146 ASSERT_WSDEQUE_INVARIANTS(pool);
147
148 elements = (StgClosurePtr *)pool->elements;
149
150 /* We have exclusive access to the structure here, so we can reset
151 bottom and top counters, and prune invalid sparks. Contents are
152 copied in-place if they are valuable, otherwise discarded. The
153 routine uses "real" indices t and b, starts by computing them
154 as the modulus size of top and bottom,
155
156 Copying:
157
158 At the beginning, the pool structure can look like this:
159 ( bottom % size >= top % size , no wrap-around)
160 t b
161 ___________***********_________________
162
163 or like this ( bottom % size < top % size, wrap-around )
164 b t
165 ***********__________******************
166 As we need to remove useless sparks anyway, we make one pass
167 between t and b, moving valuable content to b and subsequent
168 cells (wrapping around when the size is reached).
169
170 b t
171 ***********OOO_______XX_X__X?**********
172 ^____move?____/
173
174 After this movement, botInd becomes the new bottom, and old
175 bottom becomes the new top index, both as indices in the array
176 size range.
177 */
178 // starting here
179 currInd = (pool->top) & (pool->moduloSize); // mod
180
181 // copies of evacuated closures go to space from botInd on
182 // we keep oldBotInd to know when to stop
183 oldBotInd = botInd = (pool->bottom) & (pool->moduloSize); // mod
184
185 // on entry to loop, we are within the bounds
186 ASSERT( currInd < pool->size && botInd < pool->size );
187
188 while (currInd != oldBotInd ) {
189 /* must use != here, wrap-around at size
190 subtle: loop not entered if queue empty
191 */
192
193 /* check element at currInd. if valuable, evacuate and move to
194 botInd, otherwise move on */
195 spark = elements[currInd];
196
197 // We have to be careful here: in the parallel GC, another
198 // thread might evacuate this closure while we're looking at it,
199 // so grab the info pointer just once.
200 info = spark->header.info;
201 if (IS_FORWARDING_PTR(info)) {
202 tmp = (StgClosure*)UN_FORWARDING_PTR(info);
203 /* if valuable work: shift inside the pool */
204 if (closure_SHOULD_SPARK(tmp)) {
205 elements[botInd] = tmp; // keep entry (new address)
206 botInd++;
207 n++;
208 } else {
209 pruned_sparks++; // discard spark
210 cap->sparks_pruned++;
211 }
212 } else if (HEAP_ALLOCED(spark) &&
213 (Bdescr((P_)spark)->flags & BF_EVACUATED)) {
214 if (closure_SHOULD_SPARK(spark)) {
215 elements[botInd] = spark; // keep entry (new address)
216 botInd++;
217 n++;
218 } else {
219 pruned_sparks++; // discard spark
220 cap->sparks_pruned++;
221 }
222 } else {
223 pruned_sparks++; // discard spark
224 cap->sparks_pruned++;
225 }
226
227 currInd++;
228
229 // in the loop, we may reach the bounds, and instantly wrap around
230 ASSERT( currInd <= pool->size && botInd <= pool->size );
231 if ( currInd == pool->size ) { currInd = 0; }
232 if ( botInd == pool->size ) { botInd = 0; }
233
234 } // while-loop over spark pool elements
235
236 ASSERT(currInd == oldBotInd);
237
238 pool->top = oldBotInd; // where we started writing
239 pool->topBound = pool->top;
240
241 pool->bottom = (oldBotInd <= botInd) ? botInd : (botInd + pool->size);
242 // first free place we did not use (corrected by wraparound)
243
244 debugTrace(DEBUG_sparks, "pruned %d sparks", pruned_sparks);
245
246 debugTrace(DEBUG_sparks,
247 "new spark queue len=%ld; (hd=%ld; tl=%ld)",
248 sparkPoolSize(pool), pool->bottom, pool->top);
249
250 ASSERT_WSDEQUE_INVARIANTS(pool);
251 }
252
253 /* GC for the spark pool, called inside Capability.c for all
254 capabilities in turn. Blindly "evac"s complete spark pool. */
255 void
256 traverseSparkQueue (evac_fn evac, void *user, Capability *cap)
257 {
258 StgClosure **sparkp;
259 SparkPool *pool;
260 StgWord top,bottom, modMask;
261
262 pool = cap->sparks;
263
264 ASSERT_WSDEQUE_INVARIANTS(pool);
265
266 top = pool->top;
267 bottom = pool->bottom;
268 sparkp = (StgClosurePtr*)pool->elements;
269 modMask = pool->moduloSize;
270
271 while (top < bottom) {
272 /* call evac for all closures in range (wrap-around via modulo)
273 * In GHC-6.10, evac takes an additional 1st argument to hold a
274 * GC-specific register, see rts/sm/GC.c::mark_root()
275 */
276 evac( user , sparkp + (top & modMask) );
277 top++;
278 }
279
280 debugTrace(DEBUG_sparks,
281 "traversed spark queue, len=%ld; (hd=%ld; tl=%ld)",
282 sparkPoolSize(pool), pool->bottom, pool->top);
283 }
284
285 /* ----------------------------------------------------------------------------
286 * balanceSparkPoolsCaps: takes an array of capabilities (usually: all
287 * capabilities) and its size. Accesses all spark pools and equally
288 * distributes the sparks among them.
289 *
290 * Could be called after GC, before Cap. release, from scheduler.
291 * -------------------------------------------------------------------------- */
292 void balanceSparkPoolsCaps(nat n_caps, Capability caps[])
293 GNUC3_ATTRIBUTE(__noreturn__);
294
295 void balanceSparkPoolsCaps(nat n_caps STG_UNUSED,
296 Capability caps[] STG_UNUSED) {
297 barf("not implemented");
298 }
299
300 #else
301
302 StgInt
303 newSpark (StgRegTable *reg STG_UNUSED, StgClosure *p STG_UNUSED)
304 {
305 /* nothing */
306 return 1;
307 }
308
309 #endif /* THREADED_RTS */