source: libcfa/src/concurrency/preemption.cfa@ 342be43

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since 342be43 was e235429, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Removed last parker/unparker information is it was not particularly useful
  • Property mode set to 100644
File size: 17.3 KB
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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author : Thierry Delisle
10// Created On : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Wed Aug 26 16:46:03 2020
13// Update Count : 53
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21#include <errno.h>
22#include <stdio.h>
23#include <string.h>
24#include <unistd.h>
25#include <limits.h> // PTHREAD_STACK_MIN
26
27#include "bits/signal.hfa"
28#include "kernel_private.hfa"
29
30#if !defined(__CFA_DEFAULT_PREEMPTION__)
31#define __CFA_DEFAULT_PREEMPTION__ 10`ms
32#endif
33
34Duration default_preemption() __attribute__((weak)) {
35 return __CFA_DEFAULT_PREEMPTION__;
36}
37
38// FwdDeclarations : timeout handlers
39static void preempt( processor * this );
40static void timeout( struct __processor_id_t * id, $thread * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_alarm ( __CFA_SIGPARMS__ );
45static void sigHandler_segv ( __CFA_SIGPARMS__ );
46static void sigHandler_ill ( __CFA_SIGPARMS__ );
47static void sigHandler_fpe ( __CFA_SIGPARMS__ );
48static void sigHandler_abort ( __CFA_SIGPARMS__ );
49
50// FwdDeclarations : alarm thread main
51static void * alarm_loop( __attribute__((unused)) void * args );
52
53// Machine specific register name
54#if defined( __i386 )
55#define CFA_REG_IP gregs[REG_EIP]
56#elif defined( __x86_64 )
57#define CFA_REG_IP gregs[REG_RIP]
58#elif defined( __arm__ )
59#define CFA_REG_IP arm_pc
60#elif defined( __aarch64__ )
61#define CFA_REG_IP pc
62#else
63#error unsupported hardware architecture
64#endif
65
66KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
67event_kernel_t * event_kernel; // kernel public handle to even kernel
68static pthread_t alarm_thread; // pthread handle to alarm thread
69static void * alarm_stack; // pthread stack for alarm thread
70
71static void ?{}(event_kernel_t & this) with( this ) {
72 alarms{};
73 lock{};
74}
75
76enum {
77 PREEMPT_NORMAL = 0,
78 PREEMPT_TERMINATE = 1,
79};
80
81//=============================================================================================
82// Kernel Preemption logic
83//=============================================================================================
84
85// Get next expired node
86static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
88 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
89 return pop(alarms); // Otherwise just pop head
90}
91
92// Tick one frame of the Discrete Event Simulation for alarms
93static void tick_preemption( struct __processor_id_t * id ) {
94 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
95 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
96 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
97
98 //Loop throught every thing expired
99 while( node = get_expired( alarms, currtime ) ) {
100 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101 Duration period = node->period;
102 if( period == 0) {
103 node->set = false; // Node is one-shot, just mark it as not pending
104 }
105
106 // Check if this is a kernel
107 if( node->kernel_alarm ) {
108 preempt( node->proc );
109 }
110 else {
111 timeout( id, node->thrd );
112 }
113
114 // Check if this is a periodic alarm
115 if( period > 0 ) {
116 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
117 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
118 insert( alarms, node ); // Reinsert the node for the next time it triggers
119 }
120 }
121
122 // If there are still alarms pending, reset the timer
123 if( & (*alarms)`first ) {
124 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
125 Duration delta = (*alarms)`first.alarm - currtime;
126 Duration capped = max(delta, 50`us);
127 // itimerval tim = { caped };
128 // __cfaabi_dbg_print_buffer_local( " Values are %lu, %lu, %lu %lu.\n", delta.tv, caped.tv, tim.it_value.tv_sec, tim.it_value.tv_usec);
129
130 __kernel_set_timer( capped );
131 }
132}
133
134// Update the preemption of a processor and notify interested parties
135void update_preemption( processor * this, Duration duration ) {
136 alarm_node_t * alarm = this->preemption_alarm;
137
138 // Alarms need to be enabled
139 if ( duration > 0 && ! alarm->set ) {
140 alarm->alarm = __kernel_get_time() + duration;
141 alarm->period = duration;
142 register_self( alarm );
143 }
144 // Zero duration but alarm is set
145 else if ( duration == 0 && alarm->set ) {
146 unregister_self( alarm );
147 alarm->alarm = 0;
148 alarm->period = 0;
149 }
150 // If alarm is different from previous, change it
151 else if ( duration > 0 && alarm->period != duration ) {
152 unregister_self( alarm );
153 alarm->alarm = __kernel_get_time() + duration;
154 alarm->period = duration;
155 register_self( alarm );
156 }
157}
158
159//=============================================================================================
160// Kernel Signal Tools
161//=============================================================================================
162
163__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
164
165extern "C" {
166 // Disable interrupts by incrementing the counter
167 void disable_interrupts() {
168 with( kernelTLS.preemption_state ) {
169 #if GCC_VERSION > 50000
170 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
171 #endif
172
173 // Set enabled flag to false
174 // should be atomic to avoid preemption in the middle of the operation.
175 // use memory order RELAXED since there is no inter-thread on this variable requirements
176 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
177
178 // Signal the compiler that a fence is needed but only for signal handlers
179 __atomic_signal_fence(__ATOMIC_ACQUIRE);
180
181 __attribute__((unused)) unsigned short new_val = disable_count + 1;
182 disable_count = new_val;
183 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
184 }
185 }
186
187 // Enable interrupts by decrementing the counter
188 // If counter reaches 0, execute any pending __cfactx_switch
189 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
190 processor * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
191 /* paranoid */ verify( proc );
192
193 with( kernelTLS.preemption_state ){
194 unsigned short prev = disable_count;
195 disable_count -= 1;
196 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
197
198 // Check if we need to prempt the thread because an interrupt was missed
199 if( prev == 1 ) {
200 #if GCC_VERSION > 50000
201 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
202 #endif
203
204 // Set enabled flag to true
205 // should be atomic to avoid preemption in the middle of the operation.
206 // use memory order RELAXED since there is no inter-thread on this variable requirements
207 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
208
209 // Signal the compiler that a fence is needed but only for signal handlers
210 __atomic_signal_fence(__ATOMIC_RELEASE);
211 if( proc->pending_preemption ) {
212 proc->pending_preemption = false;
213 force_yield( __POLL_PREEMPTION );
214 }
215 }
216 }
217
218 // For debugging purposes : keep track of the last person to enable the interrupts
219 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
220 }
221
222 // Disable interrupts by incrementint the counter
223 // Don't execute any pending __cfactx_switch even if counter reaches 0
224 void enable_interrupts_noPoll() {
225 unsigned short prev = kernelTLS.preemption_state.disable_count;
226 kernelTLS.preemption_state.disable_count -= 1;
227 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
228 if( prev == 1 ) {
229 #if GCC_VERSION > 50000
230 static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
231 #endif
232 // Set enabled flag to true
233 // should be atomic to avoid preemption in the middle of the operation.
234 // use memory order RELAXED since there is no inter-thread on this variable requirements
235 __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
236
237 // Signal the compiler that a fence is needed but only for signal handlers
238 __atomic_signal_fence(__ATOMIC_RELEASE);
239 }
240 }
241}
242
243// sigprocmask wrapper : unblock a single signal
244static inline void signal_unblock( int sig ) {
245 sigset_t mask;
246 sigemptyset( &mask );
247 sigaddset( &mask, sig );
248
249 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
250 abort( "internal error, pthread_sigmask" );
251 }
252}
253
254// sigprocmask wrapper : block a single signal
255static inline void signal_block( int sig ) {
256 sigset_t mask;
257 sigemptyset( &mask );
258 sigaddset( &mask, sig );
259
260 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
261 abort( "internal error, pthread_sigmask" );
262 }
263}
264
265// kill wrapper : signal a processor
266static void preempt( processor * this ) {
267 sigval_t value = { PREEMPT_NORMAL };
268 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
269}
270
271// reserved for future use
272static void timeout( struct __processor_id_t * id, $thread * this ) {
273 #if !defined( __CFA_NO_STATISTICS__ )
274 kernelTLS.this_stats = this->curr_cluster->stats;
275 #endif
276 __unpark( id, this );
277}
278
279// KERNEL ONLY
280// Check if a __cfactx_switch signal handler shoud defer
281// If true : preemption is safe
282// If false : preemption is unsafe and marked as pending
283static inline bool preemption_ready() {
284 // Check if preemption is safe
285 bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
286
287 // Adjust the pending flag accordingly
288 kernelTLS.this_processor->pending_preemption = !ready;
289 return ready;
290}
291
292//=============================================================================================
293// Kernel Signal Startup/Shutdown logic
294//=============================================================================================
295
296// Startup routine to activate preemption
297// Called from kernel_startup
298void __kernel_alarm_startup() {
299 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
300
301 // Start with preemption disabled until ready
302 kernelTLS.preemption_state.enabled = false;
303 kernelTLS.preemption_state.disable_count = 1;
304
305 // Initialize the event kernel
306 event_kernel = (event_kernel_t *)&storage_event_kernel;
307 (*event_kernel){};
308
309 // Setup proper signal handlers
310 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
311 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
312
313 signal_block( SIGALRM );
314
315 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
316}
317
318// Shutdown routine to deactivate preemption
319// Called from kernel_shutdown
320void __kernel_alarm_shutdown() {
321 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
322
323 // Block all signals since we are already shutting down
324 sigset_t mask;
325 sigfillset( &mask );
326 sigprocmask( SIG_BLOCK, &mask, 0p );
327
328 // Notify the alarm thread of the shutdown
329 sigval val = { 1 };
330 pthread_sigqueue( alarm_thread, SIGALRM, val );
331
332 // Wait for the preemption thread to finish
333
334 pthread_join( alarm_thread, 0p );
335 free( alarm_stack );
336
337 // Preemption is now fully stopped
338
339 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
340}
341
342// Raii ctor/dtor for the preemption_scope
343// Used by thread to control when they want to receive preemption signals
344void ?{}( preemption_scope & this, processor * proc ) {
345 (this.alarm){ proc, (Time){ 0 }, 0`s };
346 this.proc = proc;
347 this.proc->preemption_alarm = &this.alarm;
348
349 update_preemption( this.proc, this.proc->cltr->preemption_rate );
350}
351
352void ^?{}( preemption_scope & this ) {
353 disable_interrupts();
354
355 update_preemption( this.proc, 0`s );
356}
357
358//=============================================================================================
359// Kernel Signal Handlers
360//=============================================================================================
361
362// Context switch signal handler
363// Receives SIGUSR1 signal and causes the current thread to yield
364static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
365 __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
366
367 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
368 // the interrupt that is supposed to force the kernel thread to preempt might arrive
369 // before the kernel thread has even started running. When that happens, an interrupt
370 // with a null 'this_processor' will be caught, just ignore it.
371 if(! kernelTLS.this_processor ) return;
372
373 choose(sfp->si_value.sival_int) {
374 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
375 case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
376 default:
377 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
378 }
379
380 // Check if it is safe to preempt here
381 if( !preemption_ready() ) { return; }
382
383 __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", kernelTLS.this_processor, kernelTLS.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
384
385 // Sync flag : prevent recursive calls to the signal handler
386 kernelTLS.preemption_state.in_progress = true;
387
388 // Clear sighandler mask before context switching.
389 #if GCC_VERSION > 50000
390 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
391 #endif
392 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
393 abort( "internal error, sigprocmask" );
394 }
395
396 // TODO: this should go in finish action
397 // Clear the in progress flag
398 kernelTLS.preemption_state.in_progress = false;
399
400 // Preemption can occur here
401
402 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
403}
404
405static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
406 abort("SIGALRM should never reach the signal handler");
407}
408
409// Main of the alarm thread
410// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
411static void * alarm_loop( __attribute__((unused)) void * args ) {
412 __processor_id_t id;
413 id.full_proc = false;
414 id.id = doregister(&id);
415
416 // Block sigalrms to control when they arrive
417 sigset_t mask;
418 sigfillset(&mask);
419 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
420 abort( "internal error, pthread_sigmask" );
421 }
422
423 sigemptyset( &mask );
424 sigaddset( &mask, SIGALRM );
425
426 // Main loop
427 while( true ) {
428 // Wait for a sigalrm
429 siginfo_t info;
430 int sig = sigwaitinfo( &mask, &info );
431
432 if( sig < 0 ) {
433 //Error!
434 int err = errno;
435 switch( err ) {
436 case EAGAIN :
437 case EINTR :
438 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
439 continue;
440 case EINVAL :
441 abort( "Timeout was invalid." );
442 default:
443 abort( "Unhandled error %d", err);
444 }
445 }
446
447 // If another signal arrived something went wrong
448 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
449
450 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
451 // Switch on the code (a.k.a. the sender) to
452 switch( info.si_code )
453 {
454 // Timers can apparently be marked as sent for the kernel
455 // In either case, tick preemption
456 case SI_TIMER:
457 case SI_KERNEL:
458 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
459 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
460 tick_preemption( &id );
461 unlock( event_kernel->lock );
462 break;
463 // Signal was not sent by the kernel but by an other thread
464 case SI_QUEUE:
465 // For now, other thread only signal the alarm thread to shut it down
466 // If this needs to change use info.si_value and handle the case here
467 goto EXIT;
468 }
469 }
470
471EXIT:
472 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
473 unregister(&id);
474 return 0p;
475}
476
477//=============================================================================================
478// Kernel Signal Debug
479//=============================================================================================
480
481void __cfaabi_check_preemption() {
482 bool ready = kernelTLS.preemption_state.enabled;
483 if(!ready) { abort("Preemption should be ready"); }
484
485 sigset_t oldset;
486 int ret;
487 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
488 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
489
490 ret = sigismember(&oldset, SIGUSR1);
491 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
492 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
493
494 ret = sigismember(&oldset, SIGALRM);
495 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
496 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
497
498 ret = sigismember(&oldset, SIGTERM);
499 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
500 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
501}
502
503#ifdef __CFA_WITH_VERIFY__
504bool __cfaabi_dbg_in_kernel() {
505 return !kernelTLS.preemption_state.enabled;
506}
507#endif
508
509// Local Variables: //
510// mode: c //
511// tab-width: 4 //
512// End: //
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