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comparison MasterLoop.c @ 208:eaf7e4c58c9e

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Create common_ancestor brch -- all branches will be closed, then new ones created with this as the common ancestor of all branches -- it is incomplete! only code that is common to all HW and Feat and FeatDev branches is in here
author Some Random Person <seanhalle@yahoo.com>
date Wed, 22 Feb 2012 11:39:12 -0800
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children 0c83ea8adefc
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1 /*
2 * Copyright 2010 OpenSourceStewardshipFoundation
3 *
4 * Licensed under BSD
5 */
6
7
8
9 #include <stdio.h>
10 #include <stddef.h>
11
12 #include "VMS.h"
13 #include "ProcrContext.h"
14
15
16 //===========================================================================
17 void inline
18 stealWorkInto( SchedSlot *currSlot, VMSQueueStruc *readyToAnimateQ,
19 SlaveVP *masterPr );
20
21 //===========================================================================
22
23
24
25 /*This code is animated by the virtual Master processor.
26 *
27 *Polls each sched slot exactly once, hands any requests made by a newly
28 * done slave to the "request handler" plug-in function
29 *
30 *Any slots that need a virt procr assigned are given to the "schedule"
31 * plug-in function, which tries to assign a virt procr (slave) to it.
32 *
33 *When all slots needing a processor have been given to the schedule plug-in,
34 * a fraction of the procrs successfully scheduled are put into the
35 * work queue, then a continuation of this function is put in, then the rest
36 * of the virt procrs that were successfully scheduled.
37 *
38 *The first thing the continuation does is busy-wait until the previous
39 * animation completes. This is because an (unlikely) continuation may
40 * sneak through queue before previous continuation is done putting second
41 * part of scheduled slaves in, which is the only race condition.
42 *
43 */
44
45 /*May 29, 2010 -- birth a Master during init so that first core loop to
46 * start running gets it and does all the stuff for a newly born --
47 * from then on, will be doing continuation, but do suspension self
48 * directly at end of master loop
49 *So VMS__init just births the master virtual processor same way it births
50 * all the others -- then does any extra setup needed and puts it into the
51 * work queue.
52 *However means have to make masterEnv a global static volatile the same way
53 * did with readyToAnimateQ in core loop. -- for performance, put the
54 * jump to the core loop directly in here, and have it directly jump back.
55 *
56 *
57 *Aug 18, 2010 -- Going to a separate MasterVP for each core, to see if this
58 * avoids the suspected bug in the system stack that causes bizarre faults
59 * at random places in the system code.
60 *
61 *So, this function is coupled to each of the MasterVPs, -- meaning this
62 * function can't rely on a particular stack and frame -- each MasterVP that
63 * animates this function has a different one.
64 *
65 *At this point, the masterLoop does not write itself into the queue anymore,
66 * instead, the coreLoop acquires the masterLock when it has nothing to
67 * animate, and then animates its own masterLoop. However, still try to put
68 * several AppVPs into the queue to amortize the startup cost of switching
69 * to the MasterVP. Note, don't have to worry about latency of requests much
70 * because most requests generate work for same core -- only latency issue
71 * is case when other cores starved and one core's requests generate work
72 * for them -- so keep max in queue to 3 or 4..
73 */
74 void masterLoop( void *initData, SlaveVP *animatingPr )
75 {
76 int32 slotIdx, numSlotsFilled;
77 SlaveVP *schedVirtPr;
78 SchedSlot *currSlot, **schedSlots;
79 MasterEnv *masterEnv;
80 VMSQueueStruc *readyToAnimateQ;
81
82 Sched_Assigner slaveScheduler;
83 RequestHandler requestHandler;
84 void *semanticEnv;
85
86 int32 thisCoresIdx;
87 SlaveVP *masterPr;
88 volatile SlaveVP *volatileMasterPr;
89
90 volatileMasterPr = animatingPr;
91 masterPr = (SlaveVP*)volatileMasterPr; //used to force re-define after jmp
92
93 //First animation of each MasterVP will in turn animate this part
94 // of setup code.. (VP creator sets up the stack as if this function
95 // was called normally, but actually get here by jmp)
96 //So, setup values about stack ptr, jmp pt and all that
97 //masterPr->resumeInstrPtr = &&masterLoopStartPt;
98
99
100 //Note, got rid of writing the stack and frame ptr up here, because
101 // only one
102 // core can ever animate a given MasterVP, so don't need to communicate
103 // new frame and stack ptr to the MasterVP storage before a second
104 // version of that MasterVP can get animated on a different core.
105 //Also got rid of the busy-wait.
106
107
108 //masterLoopStartPt:
109 while(1){
110
111 //============================= MEASUREMENT STUFF ========================
112 #ifdef MEAS__TIME_MASTER
113 //Total Master time includes one coreloop time -- just assume the core
114 // loop time is same for Master as for AppVPs, even though it may be
115 // smaller due to higher predictability of the fixed jmp.
116 saveLowTimeStampCountInto( masterPr->startMasterTSCLow );
117 #endif
118 //========================================================================
119
120 masterEnv = (MasterEnv*)_VMSMasterEnv;
121
122 //GCC may optimize so doesn't always re-define from frame-storage
123 masterPr = (SlaveVP*)volatileMasterPr; //just to make sure after jmp
124 thisCoresIdx = masterPr->coreAnimatedBy;
125 readyToAnimateQ = masterEnv->readyToAnimateQs[thisCoresIdx];
126 schedSlots = masterEnv->allSchedSlots[thisCoresIdx];
127
128 requestHandler = masterEnv->requestHandler;
129 slaveScheduler = masterEnv->slaveSchedAssigner;
130 semanticEnv = masterEnv->semanticEnv;
131
132
133 //Poll each slot's Done flag
134 numSlotsFilled = 0;
135 for( slotIdx = 0; slotIdx < NUM_SCHED_SLOTS; slotIdx++)
136 {
137 currSlot = schedSlots[ slotIdx ];
138
139 if( currSlot->workIsDone )
140 {
141 currSlot->workIsDone = FALSE;
142 currSlot->needsProcrAssigned = TRUE;
143
144 //process requests from slave to master
145 //====================== MEASUREMENT STUFF ===================
146 #ifdef MEAS__TIME_PLUGIN
147 int32 startStamp1, endStamp1;
148 saveLowTimeStampCountInto( startStamp1 );
149 #endif
150 //============================================================
151 (*requestHandler)( currSlot->procrAssignedToSlot, semanticEnv );
152 //====================== MEASUREMENT STUFF ===================
153 #ifdef MEAS__TIME_PLUGIN
154 saveLowTimeStampCountInto( endStamp1 );
155 addIntervalToHist( startStamp1, endStamp1,
156 _VMSMasterEnv->reqHdlrLowTimeHist );
157 addIntervalToHist( startStamp1, endStamp1,
158 _VMSMasterEnv->reqHdlrHighTimeHist );
159 #endif
160 //============================================================
161 }
162 if( currSlot->needsProcrAssigned )
163 { //give slot a new virt procr
164 schedVirtPr =
165 (*slaveScheduler)( semanticEnv, thisCoresIdx );
166
167 if( schedVirtPr != NULL )
168 { currSlot->procrAssignedToSlot = schedVirtPr;
169 schedVirtPr->schedSlot = currSlot;
170 currSlot->needsProcrAssigned = FALSE;
171 numSlotsFilled += 1;
172
173 writeVMSQ( schedVirtPr, readyToAnimateQ );
174 }
175 }
176 }
177
178
179 #ifdef USE_WORK_STEALING
180 //If no slots filled, means no more work, look for work to steal.
181 if( numSlotsFilled == 0 )
182 { gateProtected_stealWorkInto( currSlot, readyToAnimateQ, masterPr );
183 }
184 #endif
185
186
187 #ifdef MEAS__TIME_MASTER
188 saveLowTimeStampCountInto( masterPr->endMasterTSCLow );
189 #endif
190
191 masterSwitchToCoreLoop(animatingPr);
192 flushRegisters();
193 }//MasterLoop
194
195
196 }
197
198
199
200 /*This has a race condition -- the coreloops are accessing their own queues
201 * at the same time that this work-stealer on a different core is trying to
202 */
203 void inline
204 stealWorkInto( SchedSlot *currSlot, VMSQueueStruc *readyToAnimateQ,
205 SlaveVP *masterPr )
206 {
207 SlaveVP *stolenPr;
208 int32 coreIdx, i;
209 VMSQueueStruc *currQ;
210
211 stolenPr = NULL;
212 coreIdx = masterPr->coreAnimatedBy;
213 for( i = 0; i < NUM_CORES -1; i++ )
214 {
215 if( coreIdx >= NUM_CORES -1 )
216 { coreIdx = 0;
217 }
218 else
219 { coreIdx++;
220 }
221 currQ = _VMSMasterEnv->readyToAnimateQs[coreIdx];
222 if( numInVMSQ( currQ ) > 0 )
223 { stolenPr = readVMSQ (currQ );
224 break;
225 }
226 }
227
228 if( stolenPr != NULL )
229 { currSlot->procrAssignedToSlot = stolenPr;
230 stolenPr->schedSlot = currSlot;
231 currSlot->needsProcrAssigned = FALSE;
232
233 writeVMSQ( stolenPr, readyToAnimateQ );
234 }
235 }
236
237 /*This algorithm makes the common case fast. Make the coreloop passive,
238 * and show its progress. Make the stealer control a gate that coreloop
239 * has to pass.
240 *To avoid interference, only one stealer at a time. Use a global
241 * stealer-lock.
242 *
243 *The pattern is based on a gate -- stealer shuts the gate, then monitors
244 * to be sure any already past make it all the way out, before starting.
245 *So, have a "progress" measure just before the gate, then have two after it,
246 * one is in a "waiting room" outside the gate, the other is at the exit.
247 *Then, the stealer first shuts the gate, then checks the progress measure
248 * outside it, then looks to see if the progress measure at the exit is the
249 * same. If yes, it knows the protected area is empty 'cause no other way
250 * to get in and the last to get in also exited.
251 *If the progress measure at the exit is not the same, then the stealer goes
252 * into a loop checking both the waiting-area and the exit progress-measures
253 * until one of them shows the same as the measure outside the gate. Might
254 * as well re-read the measure outside the gate each go around, just to be
255 * sure. It is guaranteed that one of the two will eventually match the one
256 * outside the gate.
257 *
258 *Here's an informal proof of correctness:
259 *The gate can be closed at any point, and have only four cases:
260 * 1) coreloop made it past the gate-closing but not yet past the exit
261 * 2) coreloop made it past the pre-gate progress update but not yet past
262 * the gate,
263 * 3) coreloop is right before the pre-gate update
264 * 4) coreloop is past the exit and far from the pre-gate update.
265 *
266 * Covering the cases in reverse order,
267 * 4) is not a problem -- stealer will read pre-gate progress, see that it
268 * matches exit progress, and the gate is closed, so stealer can proceed.
269 * 3) stealer will read pre-gate progress just after coreloop updates it..
270 * so stealer goes into a loop until the coreloop causes wait-progress
271 * to match pre-gate progress, so then stealer can proceed
272 * 2) same as 3..
273 * 1) stealer reads pre-gate progress, sees that it's different than exit,
274 * so goes into loop until exit matches pre-gate, now it knows coreloop
275 * is not in protected and cannot get back in, so can proceed.
276 *
277 *Implementation for the stealer:
278 *
279 *First, acquire the stealer lock -- only cores with no work to do will
280 * compete to steal, so not a big performance penalty having only one --
281 * will rarely have multiple stealers in a system with plenty of work -- and
282 * in a system with little work, it doesn't matter.
283 *
284 *Note, have single-reader, single-writer pattern for all variables used to
285 * communicate between stealer and victims
286 *
287 *So, scan the queues of the core loops, until find non-empty. Each core
288 * has its own list that it scans. The list goes in order from closest to
289 * furthest core, so it steals first from close cores. Later can add
290 * taking info from the app about overlapping footprints, and scan all the
291 * others then choose work with the most footprint overlap with the contents
292 * of this core's cache.
293 *
294 *Now, have a victim want to take work from. So, shut the gate in that
295 * coreloop, by setting the "gate closed" var on its stack to TRUE.
296 *Then, read the core's pre-gate progress and compare to the core's exit
297 * progress.
298 *If same, can proceed to take work from the coreloop's queue. When done,
299 * write FALSE to gate closed var.
300 *If different, then enter a loop that reads the pre-gate progress, then
301 * compares to exit progress then to wait progress. When one of two
302 * matches, proceed. Take work from the coreloop's queue. When done,
303 * write FALSE to the gate closed var.
304 *
305 */
306 void inline
307 gateProtected_stealWorkInto( SchedSlot *currSlot,
308 VMSQueueStruc *myReadyToAnimateQ,
309 SlaveVP *masterPr )
310 {
311 SlaveVP *stolenPr;
312 int32 coreIdx, i, haveAVictim, gotLock;
313 VMSQueueStruc *victimsQ;
314
315 volatile GateStruc *vicGate;
316 int32 coreMightBeInProtected;
317
318
319
320 //see if any other cores have work available to steal
321 haveAVictim = FALSE;
322 coreIdx = masterPr->coreAnimatedBy;
323 for( i = 0; i < NUM_CORES -1; i++ )
324 {
325 if( coreIdx >= NUM_CORES -1 )
326 { coreIdx = 0;
327 }
328 else
329 { coreIdx++;
330 }
331 victimsQ = _VMSMasterEnv->readyToAnimateQs[coreIdx];
332 if( numInVMSQ( victimsQ ) > 0 )
333 { haveAVictim = TRUE;
334 vicGate = _VMSMasterEnv->workStealingGates[ coreIdx ];
335 break;
336 }
337 }
338 if( !haveAVictim ) return; //no work to steal, exit
339
340 //have a victim core, now get the stealer-lock
341 gotLock =__sync_bool_compare_and_swap( &(_VMSMasterEnv->workStealingLock),
342 UNLOCKED, LOCKED );
343 if( !gotLock ) return; //go back to core loop, which will re-start master
344
345
346 //====== Start Gate-protection =======
347 vicGate->gateClosed = TRUE;
348 coreMightBeInProtected= vicGate->preGateProgress != vicGate->exitProgress;
349 while( coreMightBeInProtected )
350 { //wait until sure
351 if( vicGate->preGateProgress == vicGate->waitProgress )
352 coreMightBeInProtected = FALSE;
353 if( vicGate->preGateProgress == vicGate->exitProgress )
354 coreMightBeInProtected = FALSE;
355 }
356
357 stolenPr = readVMSQ ( victimsQ );
358
359 vicGate->gateClosed = FALSE;
360 //======= End Gate-protection =======
361
362
363 if( stolenPr != NULL ) //victim could have been in protected and taken
364 { currSlot->procrAssignedToSlot = stolenPr;
365 stolenPr->schedSlot = currSlot;
366 currSlot->needsProcrAssigned = FALSE;
367
368 writeVMSQ( stolenPr, myReadyToAnimateQ );
369 }
370
371 //unlock the work stealing lock
372 _VMSMasterEnv->workStealingLock = UNLOCKED;
373 }