source: src/libcfa/concurrency/preemption.c @ d0a045c

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerresolv-newwith_gc
Last change on this file since d0a045c was d0a045c, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Faster (but maybe unsafe) interupt management

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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 : Tue Jan 23 17:59:30 2018
13// Update Count     : 7
14//
15
16#include "preemption.h"
17
18#define ftype `ftype`
19extern "C" {
20#include <errno.h>
21#include <stdio.h>
22#include <string.h>
23#include <unistd.h>
24}
25#undef ftype
26
27#include "bits/signal.h"
28
29//TODO move to defaults
30#define __CFA_DEFAULT_PREEMPTION__ 10000
31
32//TODO move to defaults
33__attribute__((weak)) unsigned int default_preemption() {
34        return __CFA_DEFAULT_PREEMPTION__;
35}
36
37// FwdDeclarations : timeout handlers
38static void preempt( processor   * this );
39static void timeout( thread_desc * this );
40
41// FwdDeclarations : Signal handlers
42void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
43void sigHandler_segv     ( __CFA_SIGPARMS__ );
44void sigHandler_abort    ( __CFA_SIGPARMS__ );
45
46// FwdDeclarations : alarm thread main
47void * alarm_loop( __attribute__((unused)) void * args );
48
49// Machine specific register name
50#if   defined(__x86_64__)
51#define CFA_REG_IP gregs[REG_RIP]
52#elif defined(__i386__)
53#define CFA_REG_IP gregs[REG_EIP]
54#elif defined(__ARM_ARCH__)
55#define CFA_REG_IP arm_pc
56#endif
57
58KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
59event_kernel_t * event_kernel;                        // kernel public handle to even kernel
60static pthread_t alarm_thread;                        // pthread handle to alarm thread
61
62void ?{}(event_kernel_t & this) with( this ) {
63        alarms{};
64        lock{};
65}
66
67//=============================================================================================
68// Kernel Preemption logic
69//=============================================================================================
70
71// Get next expired node
72static inline alarm_node_t * get_expired( alarm_list_t * alarms, __cfa_time_t currtime ) {
73        if( !alarms->head ) return NULL;                          // If no alarms return null
74        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
75        return pop(alarms);                                       // Otherwise just pop head
76}
77
78// Tick one frame of the Discrete Event Simulation for alarms
79void tick_preemption() {
80        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
81        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
82        __cfa_time_t currtime = __kernel_get_time();    // Check current time once so we everything "happens at once"
83
84        //Loop throught every thing expired
85        while( node = get_expired( alarms, currtime ) ) {
86
87                // Check if this is a kernel
88                if( node->kernel_alarm ) {
89                        preempt( node->proc );
90                }
91                else {
92                        timeout( node->thrd );
93                }
94
95                // Check if this is a periodic alarm
96                __cfa_time_t period = node->period;
97                if( period > 0 ) {
98                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
99                        insert( alarms, node );             // Reinsert the node for the next time it triggers
100                }
101                else {
102                        node->set = false;                  // Node is one-shot, just mark it as not pending
103                }
104        }
105
106        // If there are still alarms pending, reset the timer
107        if( alarms->head ) { __kernel_set_timer( alarms->head->alarm - currtime ); }
108}
109
110// Update the preemption of a processor and notify interested parties
111void update_preemption( processor * this, __cfa_time_t duration ) {
112        alarm_node_t * alarm = this->preemption_alarm;
113
114        // Alarms need to be enabled
115        if ( duration > 0 && !alarm->set ) {
116                alarm->alarm = __kernel_get_time() + duration;
117                alarm->period = duration;
118                register_self( alarm );
119        }
120        // Zero duraction but alarm is set
121        else if ( duration == 0 && alarm->set ) {
122                unregister_self( alarm );
123                alarm->alarm = 0;
124                alarm->period = 0;
125        }
126        // If alarm is different from previous, change it
127        else if ( duration > 0 && alarm->period != duration ) {
128                unregister_self( alarm );
129                alarm->alarm = __kernel_get_time() + duration;
130                alarm->period = duration;
131                register_self( alarm );
132        }
133}
134
135//=============================================================================================
136// Kernel Signal Tools
137//=============================================================================================
138
139__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
140
141extern "C" {
142        // Disable interrupts by incrementing the counter
143        void disable_interrupts() {
144                preemption_enabled = false;
145                __attribute__((unused)) unsigned short new_val = disable_preempt_count + 1;
146                disable_preempt_count = new_val;
147                verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
148        }
149
150        // Enable interrupts by decrementing the counter
151        // If counter reaches 0, execute any pending CtxSwitch
152        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
153                processor   * proc = this_processor;      // Cache the processor now since interrupts can start happening after the atomic add
154                thread_desc * thrd = this_thread;         // Cache the thread now since interrupts can start happening after the atomic add
155
156                unsigned short prev = disable_preempt_count;
157                disable_preempt_count -= 1;
158                verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
159
160                // Check if we need to prempt the thread because an interrupt was missed
161                if( prev == 1 ) {
162                        preemption_enabled = true;
163                        if( proc->pending_preemption ) {
164                                proc->pending_preemption = false;
165                                BlockInternal( thrd );
166                        }
167                }
168
169                // For debugging purposes : keep track of the last person to enable the interrupts
170                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
171        }
172
173        // Disable interrupts by incrementint the counter
174        // Don't execute any pending CtxSwitch even if counter reaches 0
175        void enable_interrupts_noPoll() {
176                unsigned short prev = disable_preempt_count;
177                disable_preempt_count -= 1;
178                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
179                if( prev == 1 ) {
180                        preemption_enabled = true;
181                }
182        }
183}
184
185// sigprocmask wrapper : unblock a single signal
186static inline void signal_unblock( int sig ) {
187        sigset_t mask;
188        sigemptyset( &mask );
189        sigaddset( &mask, sig );
190
191        if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
192            abortf( "internal error, pthread_sigmask" );
193        }
194}
195
196// sigprocmask wrapper : block a single signal
197static inline void signal_block( int sig ) {
198        sigset_t mask;
199        sigemptyset( &mask );
200        sigaddset( &mask, sig );
201
202        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
203            abortf( "internal error, pthread_sigmask" );
204        }
205}
206
207// kill wrapper : signal a processor
208static void preempt( processor * this ) {
209        pthread_kill( this->kernel_thread, SIGUSR1 );
210}
211
212// reserved for future use
213static void timeout( thread_desc * this ) {
214        //TODO : implement waking threads
215}
216
217
218// Check if a CtxSwitch signal handler shoud defer
219// If true  : preemption is safe
220// If false : preemption is unsafe and marked as pending
221static inline bool preemption_ready() {
222        bool ready = preemption_enabled && !preemption_in_progress; // Check if preemption is safe
223        this_processor->pending_preemption = !ready;                        // Adjust the pending flag accordingly
224        return ready;
225}
226
227//=============================================================================================
228// Kernel Signal Startup/Shutdown logic
229//=============================================================================================
230
231// Startup routine to activate preemption
232// Called from kernel_startup
233void kernel_start_preemption() {
234        __cfaabi_dbg_print_safe("Kernel : Starting preemption\n");
235
236        // Start with preemption disabled until ready
237        preemption_enabled = false;
238        disable_preempt_count = 1;
239
240        // Initialize the event kernel
241        event_kernel = (event_kernel_t *)&storage_event_kernel;
242        (*event_kernel){};
243
244        // Setup proper signal handlers
245        __kernel_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART );         // CtxSwitch handler
246
247        signal_block( SIGALRM );
248
249        pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
250}
251
252// Shutdown routine to deactivate preemption
253// Called from kernel_shutdown
254void kernel_stop_preemption() {
255        __cfaabi_dbg_print_safe("Kernel : Preemption stopping\n");
256
257        // Block all signals since we are already shutting down
258        sigset_t mask;
259        sigfillset( &mask );
260        sigprocmask( SIG_BLOCK, &mask, NULL );
261
262        // Notify the alarm thread of the shutdown
263        sigval val = { 1 };
264        pthread_sigqueue( alarm_thread, SIGALRM, val );
265
266        // Wait for the preemption thread to finish
267        pthread_join( alarm_thread, NULL );
268
269        // Preemption is now fully stopped
270
271        __cfaabi_dbg_print_safe("Kernel : Preemption stopped\n");
272}
273
274// Raii ctor/dtor for the preemption_scope
275// Used by thread to control when they want to receive preemption signals
276void ?{}( preemption_scope & this, processor * proc ) {
277        (this.alarm){ proc, zero_time, zero_time };
278        this.proc = proc;
279        this.proc->preemption_alarm = &this.alarm;
280
281        update_preemption( this.proc, from_us(this.proc->cltr->preemption) );
282}
283
284void ^?{}( preemption_scope & this ) {
285        disable_interrupts();
286
287        update_preemption( this.proc, zero_time );
288}
289
290//=============================================================================================
291// Kernel Signal Handlers
292//=============================================================================================
293
294// Context switch signal handler
295// Receives SIGUSR1 signal and causes the current thread to yield
296void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
297        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
298
299        // Check if it is safe to preempt here
300        if( !preemption_ready() ) { return; }
301
302        __cfaabi_dbg_print_buffer_decl(" KERNEL: preempting core %p (%p).\n", this_processor, this_thread);
303
304        preemption_in_progress = true;                      // Sync flag : prevent recursive calls to the signal handler
305        signal_unblock( SIGUSR1 );                          // We are about to CtxSwitch out of the signal handler, let other handlers in
306        preemption_in_progress = false;                     // Clear the in progress flag
307
308        // Preemption can occur here
309
310        BlockInternal( (thread_desc*)this_thread );         // Do the actual CtxSwitch
311}
312
313// Main of the alarm thread
314// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
315void * alarm_loop( __attribute__((unused)) void * args ) {
316        // Block sigalrms to control when they arrive
317        sigset_t mask;
318        sigemptyset( &mask );
319        sigaddset( &mask, SIGALRM );
320
321        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
322            abortf( "internal error, pthread_sigmask" );
323        }
324
325        // Main loop
326        while( true ) {
327                // Wait for a sigalrm
328                siginfo_t info;
329                int sig = sigwaitinfo( &mask, &info );
330
331                if( sig < 0 ) {
332                        //Error!
333                        int err = errno;
334                        switch( err ) {
335                                case EAGAIN :
336                                case EINTR :
337                                        continue;
338                        case EINVAL :
339                                        abortf("Timeout was invalid.");
340                                default:
341                                        abortf("Unhandled error %d", err);
342                        }
343                }
344
345                // If another signal arrived something went wrong
346                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
347
348                // __cfaabi_dbg_print_safe("Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
349                // Switch on the code (a.k.a. the sender) to
350                switch( info.si_code )
351                {
352                // Timers can apparently be marked as sent for the kernel
353                // In either case, tick preemption
354                case SI_TIMER:
355                case SI_KERNEL:
356                        // __cfaabi_dbg_print_safe("Kernel : Preemption thread tick\n");
357                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
358                        tick_preemption();
359                        unlock( event_kernel->lock );
360                        break;
361                // Signal was not sent by the kernel but by an other thread
362                case SI_QUEUE:
363                        // For now, other thread only signal the alarm thread to shut it down
364                        // If this needs to change use info.si_value and handle the case here
365                        goto EXIT;
366                }
367        }
368
369EXIT:
370        __cfaabi_dbg_print_safe("Kernel : Preemption thread stopping\n");
371        return NULL;
372}
373
374// Local Variables: //
375// mode: c //
376// tab-width: 4 //
377// End: //
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