source: src/libcfa/concurrency/preemption.c @ ae3bb3d

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerwith_gc
Last change on this file since ae3bb3d was ae3bb3d, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Merge branch 'master' of plg.uwaterloo.ca:software/cfa/cfa-cc

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File size: 16.8 KB
Line 
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 : Tue Jun  5 17:35:49 2018
13// Update Count     : 37
14//
15
16#include "preemption.h"
17#include <assert.h>
18
19extern "C" {
20#include <errno.h>
21#include <stdio.h>
22#include <string.h>
23#include <unistd.h>
24}
25
26#include "bits/signal.h"
27
28#if !defined(__CFA_DEFAULT_PREEMPTION__)
29#define __CFA_DEFAULT_PREEMPTION__ 10`ms
30#endif
31
32Duration default_preemption() __attribute__((weak)) {
33        return __CFA_DEFAULT_PREEMPTION__;
34}
35
36// FwdDeclarations : timeout handlers
37static void preempt( processor   * this );
38static void timeout( thread_desc * this );
39
40// FwdDeclarations : Signal handlers
41void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
42void sigHandler_segv     ( __CFA_SIGPARMS__ );
43void sigHandler_ill      ( __CFA_SIGPARMS__ );
44void sigHandler_fpe      ( __CFA_SIGPARMS__ );
45void sigHandler_abort    ( __CFA_SIGPARMS__ );
46
47// FwdDeclarations : alarm thread main
48void * alarm_loop( __attribute__((unused)) void * args );
49
50// Machine specific register name
51#if   defined( __i386 )
52#define CFA_REG_IP gregs[REG_EIP]
53#elif defined( __x86_64 )
54#define CFA_REG_IP gregs[REG_RIP]
55#elif defined( __ARM_ARCH )
56#define CFA_REG_IP arm_pc
57#else
58#error unknown hardware architecture
59#endif
60
61KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
62event_kernel_t * event_kernel;                        // kernel public handle to even kernel
63static pthread_t alarm_thread;                        // pthread handle to alarm thread
64
65void ?{}(event_kernel_t & this) with( this ) {
66        alarms{};
67        lock{};
68}
69
70enum {
71        PREEMPT_NORMAL    = 0,
72        PREEMPT_TERMINATE = 1,
73};
74
75//=============================================================================================
76// Kernel Preemption logic
77//=============================================================================================
78
79// Get next expired node
80static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
81        if( !alarms->head ) return NULL;                          // If no alarms return null
82        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
83        return pop(alarms);                                       // Otherwise just pop head
84}
85
86// Tick one frame of the Discrete Event Simulation for alarms
87void tick_preemption() {
88        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
89        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
90        Time currtime = __kernel_get_time();                    // Check current time once so we everything "happens at once"
91
92        //Loop throught every thing expired
93        while( node = get_expired( alarms, currtime ) ) {
94                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
95
96                // Check if this is a kernel
97                if( node->kernel_alarm ) {
98                        preempt( node->proc );
99                }
100                else {
101                        timeout( node->thrd );
102                }
103
104                // Check if this is a periodic alarm
105                Duration period = node->period;
106                if( period > 0 ) {
107                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
108                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
109                        insert( alarms, node );             // Reinsert the node for the next time it triggers
110                }
111                else {
112                        node->set = false;                  // Node is one-shot, just mark it as not pending
113                }
114        }
115
116        // If there are still alarms pending, reset the timer
117        if( alarms->head ) {
118                __cfaabi_dbg_print_buffer_decl( " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
119                Duration delta = alarms->head->alarm - currtime;
120                Duration caped = max(delta, 50`us);
121                // itimerval tim  = { caped };
122                // __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);
123
124                __kernel_set_timer( caped );
125        }
126}
127
128// Update the preemption of a processor and notify interested parties
129void update_preemption( processor * this, Duration duration ) {
130        alarm_node_t * alarm = this->preemption_alarm;
131
132        // Alarms need to be enabled
133        if ( duration > 0 && ! alarm->set ) {
134                alarm->alarm = __kernel_get_time() + duration;
135                alarm->period = duration;
136                register_self( alarm );
137        }
138        // Zero duration but alarm is set
139        else if ( duration == 0 && alarm->set ) {
140                unregister_self( alarm );
141                alarm->alarm = 0;
142                alarm->period = 0;
143        }
144        // If alarm is different from previous, change it
145        else if ( duration > 0 && alarm->period != duration ) {
146                unregister_self( alarm );
147                alarm->alarm = __kernel_get_time() + duration;
148                alarm->period = duration;
149                register_self( alarm );
150        }
151}
152
153//=============================================================================================
154// Kernel Signal Tools
155//=============================================================================================
156
157__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
158
159extern "C" {
160        // Disable interrupts by incrementing the counter
161        void disable_interrupts() {
162                with( kernelTLS.preemption_state ) {
163                        #if GCC_VERSION > 50000
164                        static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
165                        #endif
166
167                        // Set enabled flag to false
168                        // should be atomic to avoid preemption in the middle of the operation.
169                        // use memory order RELAXED since there is no inter-thread on this variable requirements
170                        __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
171
172                        // Signal the compiler that a fence is needed but only for signal handlers
173                        __atomic_signal_fence(__ATOMIC_ACQUIRE);
174
175                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
176                        disable_count = new_val;
177                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
178                }
179        }
180
181        // Enable interrupts by decrementing the counter
182        // If counter reaches 0, execute any pending CtxSwitch
183        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
184                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
185                thread_desc * thrd = kernelTLS.this_thread;       // Cache the thread now since interrupts can start happening after the atomic store
186
187                with( kernelTLS.preemption_state ){
188                        unsigned short prev = disable_count;
189                        disable_count -= 1;
190                        verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
191
192                        // Check if we need to prempt the thread because an interrupt was missed
193                        if( prev == 1 ) {
194                                #if GCC_VERSION > 50000
195                                static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
196                                #endif
197
198                                // Set enabled flag to true
199                                // should be atomic to avoid preemption in the middle of the operation.
200                                // use memory order RELAXED since there is no inter-thread on this variable requirements
201                                __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
202
203                                // Signal the compiler that a fence is needed but only for signal handlers
204                                __atomic_signal_fence(__ATOMIC_RELEASE);
205                                if( proc->pending_preemption ) {
206                                        proc->pending_preemption = false;
207                                        BlockInternal( thrd );
208                                }
209                        }
210                }
211
212                // For debugging purposes : keep track of the last person to enable the interrupts
213                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
214        }
215
216        // Disable interrupts by incrementint the counter
217        // Don't execute any pending CtxSwitch even if counter reaches 0
218        void enable_interrupts_noPoll() {
219                unsigned short prev = kernelTLS.preemption_state.disable_count;
220                kernelTLS.preemption_state.disable_count -= 1;
221                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
222                if( prev == 1 ) {
223                        #if GCC_VERSION > 50000
224                        static_assert(__atomic_always_lock_free(sizeof(kernelTLS.preemption_state.enabled), &kernelTLS.preemption_state.enabled), "Must be lock-free");
225                        #endif
226                        // Set enabled flag to true
227                        // should be atomic to avoid preemption in the middle of the operation.
228                        // use memory order RELAXED since there is no inter-thread on this variable requirements
229                        __atomic_store_n(&kernelTLS.preemption_state.enabled, true, __ATOMIC_RELAXED);
230
231                        // Signal the compiler that a fence is needed but only for signal handlers
232                        __atomic_signal_fence(__ATOMIC_RELEASE);
233                }
234        }
235}
236
237// sigprocmask wrapper : unblock a single signal
238static inline void signal_unblock( int sig ) {
239        sigset_t mask;
240        sigemptyset( &mask );
241        sigaddset( &mask, sig );
242
243        if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
244            abort( "internal error, pthread_sigmask" );
245        }
246}
247
248// sigprocmask wrapper : block a single signal
249static inline void signal_block( int sig ) {
250        sigset_t mask;
251        sigemptyset( &mask );
252        sigaddset( &mask, sig );
253
254        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
255            abort( "internal error, pthread_sigmask" );
256        }
257}
258
259// kill wrapper : signal a processor
260static void preempt( processor * this ) {
261        sigval_t value = { PREEMPT_NORMAL };
262        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
263}
264
265// kill wrapper : signal a processor
266void terminate(processor * this) {
267        disable_interrupts();
268        __atomic_store_n(&this->do_terminate, true, __ATOMIC_SEQ_CST);
269        wake( this );
270        sigval_t value = { PREEMPT_TERMINATE };
271        enable_interrupts();
272        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
273}
274
275// reserved for future use
276static void timeout( thread_desc * this ) {
277        //TODO : implement waking threads
278}
279
280// KERNEL ONLY
281// Check if a CtxSwitch signal handler shoud defer
282// If true  : preemption is safe
283// If false : preemption is unsafe and marked as pending
284static inline bool preemption_ready() {
285        // Check if preemption is safe
286        bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
287
288        // Adjust the pending flag accordingly
289        kernelTLS.this_processor->pending_preemption = !ready;
290        return ready;
291}
292
293//=============================================================================================
294// Kernel Signal Startup/Shutdown logic
295//=============================================================================================
296
297// Startup routine to activate preemption
298// Called from kernel_startup
299void kernel_start_preemption() {
300        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
301
302        // Start with preemption disabled until ready
303        kernelTLS.preemption_state.enabled = false;
304        kernelTLS.preemption_state.disable_count = 1;
305
306        // Initialize the event kernel
307        event_kernel = (event_kernel_t *)&storage_event_kernel;
308        (*event_kernel){};
309
310        // Setup proper signal handlers
311        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART );         // CtxSwitch handler
312
313        signal_block( SIGALRM );
314
315        pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
316}
317
318// Shutdown routine to deactivate preemption
319// Called from kernel_shutdown
320void kernel_stop_preemption() {
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, NULL );
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        pthread_join( alarm_thread, NULL );
334
335        // Preemption is now fully stopped
336
337        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
338}
339
340// Raii ctor/dtor for the preemption_scope
341// Used by thread to control when they want to receive preemption signals
342void ?{}( preemption_scope & this, processor * proc ) {
343        (this.alarm){ proc, (Time){ 0 }, 0`s };
344        this.proc = proc;
345        this.proc->preemption_alarm = &this.alarm;
346
347        update_preemption( this.proc, this.proc->cltr->preemption_rate );
348}
349
350void ^?{}( preemption_scope & this ) {
351        disable_interrupts();
352
353        update_preemption( this.proc, 0`s );
354}
355
356//=============================================================================================
357// Kernel Signal Handlers
358//=============================================================================================
359
360// Context switch signal handler
361// Receives SIGUSR1 signal and causes the current thread to yield
362void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
363        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
364
365        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
366        // the interrupt that is supposed to force the kernel thread to preempt might arrive
367        // before the kernel thread has even started running. When that happens an iterrupt
368        // we a null 'this_processor' will be caught, just ignore it.
369        if(! kernelTLS.this_processor ) return;
370
371        choose(sfp->si_value.sival_int) {
372                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
373                case PREEMPT_TERMINATE: verify( __atomic_load_n( &kernelTLS.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
374                default:
375                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
376        }
377
378        // Check if it is safe to preempt here
379        if( !preemption_ready() ) { return; }
380
381        __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) );
382
383        // Sync flag : prevent recursive calls to the signal handler
384        kernelTLS.preemption_state.in_progress = true;
385
386        // Clear sighandler mask before context switching.
387        #if GCC_VERSION > 50000
388        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
389        #endif
390        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), NULL ) == -1 ) {
391                abort( "internal error, sigprocmask" );
392        }
393
394        // TODO: this should go in finish action
395        // Clear the in progress flag
396        kernelTLS.preemption_state.in_progress = false;
397
398        // Preemption can occur here
399
400        BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
401}
402
403// Main of the alarm thread
404// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
405void * alarm_loop( __attribute__((unused)) void * args ) {
406        // Block sigalrms to control when they arrive
407        sigset_t mask;
408        sigfillset(&mask);
409        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
410            abort( "internal error, pthread_sigmask" );
411        }
412
413        sigemptyset( &mask );
414        sigaddset( &mask, SIGALRM );
415
416        // Main loop
417        while( true ) {
418                // Wait for a sigalrm
419                siginfo_t info;
420                int sig = sigwaitinfo( &mask, &info );
421
422                if( sig < 0 ) {
423                        //Error!
424                        int err = errno;
425                        switch( err ) {
426                                case EAGAIN :
427                                case EINTR :
428                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
429                                        continue;
430                        case EINVAL :
431                                        abort( "Timeout was invalid." );
432                                default:
433                                        abort( "Unhandled error %d", err);
434                        }
435                }
436
437                // If another signal arrived something went wrong
438                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
439
440                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
441                // Switch on the code (a.k.a. the sender) to
442                switch( info.si_code )
443                {
444                // Timers can apparently be marked as sent for the kernel
445                // In either case, tick preemption
446                case SI_TIMER:
447                case SI_KERNEL:
448                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
449                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
450                        tick_preemption();
451                        unlock( event_kernel->lock );
452                        break;
453                // Signal was not sent by the kernel but by an other thread
454                case SI_QUEUE:
455                        // For now, other thread only signal the alarm thread to shut it down
456                        // If this needs to change use info.si_value and handle the case here
457                        goto EXIT;
458                }
459        }
460
461EXIT:
462        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
463        return NULL;
464}
465
466//=============================================================================================
467// Kernel Signal Debug
468//=============================================================================================
469
470void __cfaabi_check_preemption() {
471        bool ready = kernelTLS.preemption_state.enabled;
472        if(!ready) { abort("Preemption should be ready"); }
473
474        sigset_t oldset;
475        int ret;
476        ret = pthread_sigmask(0, NULL, &oldset);
477        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
478
479        ret = sigismember(&oldset, SIGUSR1);
480        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
481        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
482
483        ret = sigismember(&oldset, SIGALRM);
484        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
485        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
486
487        ret = sigismember(&oldset, SIGTERM);
488        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
489        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
490}
491
492#ifdef __CFA_WITH_VERIFY__
493bool __cfaabi_dbg_in_kernel() {
494        return !kernelTLS.preemption_state.enabled;
495}
496#endif
497
498// Local Variables: //
499// mode: c //
500// tab-width: 4 //
501// End: //
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