source: libcfa/src/concurrency/preemption.cfa @ e235429

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since e235429 was e235429, checked in by Thierry Delisle <tdelisle@…>, 14 months ago

Removed last parker/unparker information is it was not particularly useful

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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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