Annotation of src/sys/rump/librump/rumpkern/scheduler.c, Revision 1.49
1.49 ! ad 1: /* $NetBSD: scheduler.c,v 1.48 2019/12/16 22:47:55 ad Exp $ */
1.1 pooka 2:
3: /*
1.26 pooka 4: * Copyright (c) 2010, 2011 Antti Kantee. All Rights Reserved.
1.1 pooka 5: *
6: * Redistribution and use in source and binary forms, with or without
7: * modification, are permitted provided that the following conditions
8: * are met:
9: * 1. Redistributions of source code must retain the above copyright
10: * notice, this list of conditions and the following disclaimer.
11: * 2. Redistributions in binary form must reproduce the above copyright
12: * notice, this list of conditions and the following disclaimer in the
13: * documentation and/or other materials provided with the distribution.
14: *
15: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
16: * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17: * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18: * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21: * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25: * SUCH DAMAGE.
26: */
27:
28: #include <sys/cdefs.h>
1.49 ! ad 29: __KERNEL_RCSID(0, "$NetBSD: scheduler.c,v 1.48 2019/12/16 22:47:55 ad Exp $");
1.1 pooka 30:
31: #include <sys/param.h>
1.16 pooka 32: #include <sys/atomic.h>
1.1 pooka 33: #include <sys/cpu.h>
1.2 pooka 34: #include <sys/kmem.h>
1.1 pooka 35: #include <sys/mutex.h>
1.8 pooka 36: #include <sys/namei.h>
1.1 pooka 37: #include <sys/queue.h>
38: #include <sys/select.h>
1.10 pooka 39: #include <sys/systm.h>
1.1 pooka 40:
1.42 pooka 41: #include <rump-sys/kern.h>
42:
1.1 pooka 43: #include <rump/rumpuser.h>
44:
45: static struct rumpcpu {
1.15 pooka 46: /* needed in fastpath */
1.1 pooka 47: struct cpu_info *rcpu_ci;
1.15 pooka 48: void *rcpu_prevlwp;
49:
50: /* needed in slowpath */
51: struct rumpuser_mtx *rcpu_mtx;
1.8 pooka 52: struct rumpuser_cv *rcpu_cv;
1.15 pooka 53: int rcpu_wanted;
54:
55: /* offset 20 (P=4) or 36 (P=8) here */
56:
57: /*
58: * Some stats. Not really that necessary, but we should
59: * have room. Note that these overflow quite fast, so need
60: * to be collected often.
61: */
62: unsigned int rcpu_fastpath;
63: unsigned int rcpu_slowpath;
64: unsigned int rcpu_migrated;
65:
66: /* offset 32 (P=4) or 50 (P=8) */
67:
68: int rcpu_align[0] __aligned(CACHE_LINE_SIZE);
1.8 pooka 69: } rcpu_storage[MAXCPUS];
1.28 rmind 70:
1.43 pooka 71: static inline struct rumpcpu *
72: cpuinfo_to_rumpcpu(struct cpu_info *ci)
73: {
74:
75: return &rcpu_storage[cpu_index(ci)];
76: }
77:
78: struct cpu_info rump_bootcpu;
1.44 pooka 79:
1.15 pooka 80: #define RCPULWP_BUSY ((void *)-1)
81: #define RCPULWP_WANTED ((void *)-2)
1.8 pooka 82:
1.15 pooka 83: static struct rumpuser_mtx *lwp0mtx;
84: static struct rumpuser_cv *lwp0cv;
85: static unsigned nextcpu;
1.14 pooka 86:
1.25 pooka 87: kmutex_t unruntime_lock; /* unruntime lwp lock. practically unused */
88:
1.19 pooka 89: static bool lwp0isbusy = false;
1.3 pooka 90:
1.15 pooka 91: /*
92: * Keep some stats.
93: *
94: * Keeping track of there is not really critical for speed, unless
95: * stats happen to be on a different cache line (CACHE_LINE_SIZE is
96: * really just a coarse estimate), so default for the performant case
97: * (i.e. no stats).
98: */
99: #ifdef RUMPSCHED_STATS
100: #define SCHED_FASTPATH(rcpu) rcpu->rcpu_fastpath++;
101: #define SCHED_SLOWPATH(rcpu) rcpu->rcpu_slowpath++;
102: #define SCHED_MIGRATED(rcpu) rcpu->rcpu_migrated++;
103: #else
104: #define SCHED_FASTPATH(rcpu)
105: #define SCHED_SLOWPATH(rcpu)
106: #define SCHED_MIGRATED(rcpu)
107: #endif
1.1 pooka 108:
109: struct cpu_info *
110: cpu_lookup(u_int index)
111: {
112:
1.43 pooka 113: return rcpu_storage[index].rcpu_ci;
1.1 pooka 114: }
115:
1.15 pooka 116: static inline struct rumpcpu *
117: getnextcpu(void)
118: {
119: unsigned newcpu;
120:
121: newcpu = atomic_inc_uint_nv(&nextcpu);
122: if (__predict_false(ncpu > UINT_MAX/2))
123: atomic_and_uint(&nextcpu, 0);
124: newcpu = newcpu % ncpu;
125:
126: return &rcpu_storage[newcpu];
127: }
128:
1.12 pooka 129: /* this could/should be mi_attach_cpu? */
130: void
1.22 pooka 131: rump_cpus_bootstrap(int *nump)
1.12 pooka 132: {
1.22 pooka 133: int num = *nump;
1.12 pooka 134:
1.13 pooka 135: if (num > MAXCPUS) {
1.22 pooka 136: aprint_verbose("CPU limit: %d wanted, %d (MAXCPUS) "
137: "available (adjusted)\n", num, MAXCPUS);
1.13 pooka 138: num = MAXCPUS;
139: }
140:
1.48 ad 141: cpu_setmodel("rumpcore (virtual)");
1.44 pooka 142:
1.48 ad 143: mi_cpu_init();
1.28 rmind 144:
1.20 pooka 145: /* attach first cpu for bootstrap */
1.43 pooka 146: rump_cpu_attach(&rump_bootcpu);
1.20 pooka 147: ncpu = 1;
1.22 pooka 148: *nump = num;
1.12 pooka 149: }
150:
1.1 pooka 151: void
1.20 pooka 152: rump_scheduler_init(int numcpu)
1.1 pooka 153: {
154: struct rumpcpu *rcpu;
155: struct cpu_info *ci;
156: int i;
157:
1.31 pooka 158: rumpuser_mutex_init(&lwp0mtx, RUMPUSER_MTX_SPIN);
1.3 pooka 159: rumpuser_cv_init(&lwp0cv);
1.20 pooka 160: for (i = 0; i < numcpu; i++) {
1.43 pooka 161: if (i == 0) {
162: ci = &rump_bootcpu;
163: } else {
164: ci = kmem_zalloc(sizeof(*ci), KM_SLEEP);
165: ci->ci_index = i;
166: }
167:
1.1 pooka 168: rcpu = &rcpu_storage[i];
1.12 pooka 169: rcpu->rcpu_ci = ci;
1.43 pooka 170: rcpu->rcpu_wanted = 0;
171: rumpuser_cv_init(&rcpu->rcpu_cv);
172: rumpuser_mutex_init(&rcpu->rcpu_mtx, RUMPUSER_MTX_SPIN);
173:
1.4 pooka 174: ci->ci_schedstate.spc_mutex =
1.32 pooka 175: mutex_obj_alloc(MUTEX_DEFAULT, IPL_SCHED);
1.9 pooka 176: ci->ci_schedstate.spc_flags = SPCF_RUNNING;
1.1 pooka 177: }
1.25 pooka 178:
1.32 pooka 179: mutex_init(&unruntime_lock, MUTEX_DEFAULT, IPL_SCHED);
1.1 pooka 180: }
181:
1.14 pooka 182: /*
183: * condvar ops using scheduler lock as the rumpuser interlock.
184: */
185: void
186: rump_schedlock_cv_wait(struct rumpuser_cv *cv)
187: {
1.15 pooka 188: struct lwp *l = curlwp;
1.43 pooka 189: struct rumpcpu *rcpu = cpuinfo_to_rumpcpu(l->l_cpu);
1.14 pooka 190:
1.15 pooka 191: /* mutex will be taken and released in cpu schedule/unschedule */
192: rumpuser_cv_wait(cv, rcpu->rcpu_mtx);
1.14 pooka 193: }
194:
195: int
196: rump_schedlock_cv_timedwait(struct rumpuser_cv *cv, const struct timespec *ts)
197: {
1.15 pooka 198: struct lwp *l = curlwp;
1.43 pooka 199: struct rumpcpu *rcpu = cpuinfo_to_rumpcpu(l->l_cpu);
1.14 pooka 200:
1.15 pooka 201: /* mutex will be taken and released in cpu schedule/unschedule */
202: return rumpuser_cv_timedwait(cv, rcpu->rcpu_mtx,
203: ts->tv_sec, ts->tv_nsec);
1.14 pooka 204: }
205:
1.19 pooka 206: static void
207: lwp0busy(void)
208: {
209:
210: /* busy lwp0 */
1.25 pooka 211: KASSERT(curlwp == NULL || curlwp->l_stat != LSONPROC);
1.19 pooka 212: rumpuser_mutex_enter_nowrap(lwp0mtx);
213: while (lwp0isbusy)
214: rumpuser_cv_wait_nowrap(lwp0cv, lwp0mtx);
215: lwp0isbusy = true;
216: rumpuser_mutex_exit(lwp0mtx);
217: }
218:
219: static void
220: lwp0rele(void)
221: {
222:
223: rumpuser_mutex_enter_nowrap(lwp0mtx);
224: KASSERT(lwp0isbusy == true);
225: lwp0isbusy = false;
226: rumpuser_cv_signal(lwp0cv);
227: rumpuser_mutex_exit(lwp0mtx);
228: }
229:
1.27 yamt 230: /*
231: * rump_schedule: ensure that the calling host thread has a valid lwp context.
1.33 pooka 232: * ie. ensure that curlwp != NULL. Also, ensure that there
233: * a 1:1 mapping between the lwp and rump kernel cpu.
1.27 yamt 234: */
1.1 pooka 235: void
236: rump_schedule()
237: {
1.3 pooka 238: struct lwp *l;
1.2 pooka 239:
240: /*
241: * If there is no dedicated lwp, allocate a temp one and
1.3 pooka 242: * set it to be free'd upon unschedule(). Use lwp0 context
1.15 pooka 243: * for reserving the necessary resources. Don't optimize
244: * for this case -- anyone who cares about performance will
245: * start a real thread.
1.2 pooka 246: */
1.36 pooka 247: if (__predict_true((l = curlwp) != NULL)) {
1.19 pooka 248: rump_schedule_cpu(l);
249: LWP_CACHE_CREDS(l, l->l_proc);
250: } else {
251: lwp0busy();
1.3 pooka 252:
253: /* schedule cpu and use lwp0 */
1.4 pooka 254: rump_schedule_cpu(&lwp0);
1.36 pooka 255: rump_lwproc_curlwp_set(&lwp0);
1.3 pooka 256:
1.19 pooka 257: /* allocate thread, switch to it, and release lwp0 */
1.21 pooka 258: l = rump__lwproc_alloclwp(initproc);
1.19 pooka 259: rump_lwproc_switch(l);
260: lwp0rele();
1.3 pooka 261:
1.19 pooka 262: /*
263: * mark new thread dead-on-unschedule. this
264: * means that we'll be running with l_refcnt == 0.
265: * relax, it's fine.
266: */
267: rump_lwproc_releaselwp();
1.2 pooka 268: }
269: }
270:
1.4 pooka 271: void
272: rump_schedule_cpu(struct lwp *l)
1.2 pooka 273: {
1.14 pooka 274:
275: rump_schedule_cpu_interlock(l, NULL);
276: }
277:
1.15 pooka 278: /*
279: * Schedule a CPU. This optimizes for the case where we schedule
280: * the same thread often, and we have nCPU >= nFrequently-Running-Thread
281: * (where CPU is virtual rump cpu, not host CPU).
282: */
1.14 pooka 283: void
284: rump_schedule_cpu_interlock(struct lwp *l, void *interlock)
285: {
1.1 pooka 286: struct rumpcpu *rcpu;
1.40 pooka 287: struct cpu_info *ci;
1.15 pooka 288: void *old;
289: bool domigrate;
290: bool bound = l->l_pflag & LP_BOUND;
291:
1.25 pooka 292: l->l_stat = LSRUN;
293:
1.15 pooka 294: /*
295: * First, try fastpath: if we were the previous user of the
296: * CPU, everything is in order cachewise and we can just
297: * proceed to use it.
298: *
299: * If we are a different thread (i.e. CAS fails), we must go
300: * through a memory barrier to ensure we get a truthful
301: * view of the world.
302: */
1.14 pooka 303:
1.17 pooka 304: KASSERT(l->l_target_cpu != NULL);
1.43 pooka 305: rcpu = cpuinfo_to_rumpcpu(l->l_target_cpu);
1.15 pooka 306: if (atomic_cas_ptr(&rcpu->rcpu_prevlwp, l, RCPULWP_BUSY) == l) {
1.29 pooka 307: if (interlock == rcpu->rcpu_mtx)
1.15 pooka 308: rumpuser_mutex_exit(rcpu->rcpu_mtx);
309: SCHED_FASTPATH(rcpu);
310: /* jones, you're the man */
311: goto fastlane;
312: }
1.1 pooka 313:
1.15 pooka 314: /*
315: * Else, it's the slowpath for us. First, determine if we
316: * can migrate.
317: */
318: if (ncpu == 1)
319: domigrate = false;
320: else
321: domigrate = true;
322:
323: /* Take lock. This acts as a load barrier too. */
1.29 pooka 324: if (interlock != rcpu->rcpu_mtx)
1.15 pooka 325: rumpuser_mutex_enter_nowrap(rcpu->rcpu_mtx);
326:
327: for (;;) {
328: SCHED_SLOWPATH(rcpu);
329: old = atomic_swap_ptr(&rcpu->rcpu_prevlwp, RCPULWP_WANTED);
330:
331: /* CPU is free? */
332: if (old != RCPULWP_BUSY && old != RCPULWP_WANTED) {
333: if (atomic_cas_ptr(&rcpu->rcpu_prevlwp,
334: RCPULWP_WANTED, RCPULWP_BUSY) == RCPULWP_WANTED) {
335: break;
1.8 pooka 336: }
337: }
1.15 pooka 338:
339: /*
340: * Do we want to migrate once?
341: * This may need a slightly better algorithm, or we
342: * might cache pingpong eternally for non-frequent
343: * threads.
344: */
345: if (domigrate && !bound) {
346: domigrate = false;
347: SCHED_MIGRATED(rcpu);
348: rumpuser_mutex_exit(rcpu->rcpu_mtx);
349: rcpu = getnextcpu();
350: rumpuser_mutex_enter_nowrap(rcpu->rcpu_mtx);
351: continue;
1.8 pooka 352: }
1.15 pooka 353:
354: /* Want CPU, wait until it's released an retry */
355: rcpu->rcpu_wanted++;
356: rumpuser_cv_wait_nowrap(rcpu->rcpu_cv, rcpu->rcpu_mtx);
357: rcpu->rcpu_wanted--;
1.8 pooka 358: }
1.15 pooka 359: rumpuser_mutex_exit(rcpu->rcpu_mtx);
360:
361: fastlane:
1.40 pooka 362: ci = rcpu->rcpu_ci;
363: l->l_cpu = l->l_target_cpu = ci;
1.4 pooka 364: l->l_mutex = rcpu->rcpu_ci->ci_schedstate.spc_mutex;
1.18 pooka 365: l->l_ncsw++;
1.25 pooka 366: l->l_stat = LSONPROC;
1.23 pooka 367:
1.40 pooka 368: /*
369: * No interrupts, so ci_curlwp === cpu_onproc.
370: * Okay, we could make an attempt to not set cpu_onproc
371: * in the case that an interrupt is scheduled immediately
372: * after a user proc, but leave that for later.
373: */
1.46 ad 374: ci->ci_curlwp = ci->ci_onproc = l;
1.1 pooka 375: }
376:
377: void
378: rump_unschedule()
379: {
1.36 pooka 380: struct lwp *l = curlwp;
1.24 pooka 381: #ifdef DIAGNOSTIC
382: int nlock;
383:
384: KERNEL_UNLOCK_ALL(l, &nlock);
385: KASSERT(nlock == 0);
386: #endif
1.2 pooka 387:
1.4 pooka 388: KASSERT(l->l_mutex == l->l_cpu->ci_schedstate.spc_mutex);
1.2 pooka 389: rump_unschedule_cpu(l);
1.25 pooka 390: l->l_mutex = &unruntime_lock;
391: l->l_stat = LSSTOP;
1.6 pooka 392:
393: /*
1.19 pooka 394: * Check special conditions:
395: * 1) do we need to free the lwp which just unscheduled?
396: * (locking order: lwp0, cpu)
397: * 2) do we want to clear curlwp for the current host thread
1.6 pooka 398: */
1.19 pooka 399: if (__predict_false(l->l_flag & LW_WEXIT)) {
400: lwp0busy();
401:
402: /* Now that we have lwp0, we can schedule a CPU again */
403: rump_schedule_cpu(l);
1.6 pooka 404:
1.19 pooka 405: /* switch to lwp0. this frees the old thread */
406: KASSERT(l->l_flag & LW_WEXIT);
407: rump_lwproc_switch(&lwp0);
1.6 pooka 408:
1.19 pooka 409: /* release lwp0 */
1.6 pooka 410: rump_unschedule_cpu(&lwp0);
1.25 pooka 411: lwp0.l_mutex = &unruntime_lock;
1.49 ! ad 412: lwp0.l_flag &= ~LW_RUNNING;
1.19 pooka 413: lwp0rele();
1.36 pooka 414: rump_lwproc_curlwp_clear(&lwp0);
1.6 pooka 415:
1.19 pooka 416: } else if (__predict_false(l->l_flag & LW_RUMP_CLEAR)) {
1.36 pooka 417: rump_lwproc_curlwp_clear(l);
1.19 pooka 418: l->l_flag &= ~LW_RUMP_CLEAR;
1.2 pooka 419: }
420: }
421:
422: void
423: rump_unschedule_cpu(struct lwp *l)
424: {
1.8 pooka 425:
1.14 pooka 426: rump_unschedule_cpu_interlock(l, NULL);
427: }
428:
429: void
430: rump_unschedule_cpu_interlock(struct lwp *l, void *interlock)
431: {
432:
1.8 pooka 433: if ((l->l_pflag & LP_INTR) == 0)
434: rump_softint_run(l->l_cpu);
1.14 pooka 435: rump_unschedule_cpu1(l, interlock);
1.8 pooka 436: }
437:
438: void
1.14 pooka 439: rump_unschedule_cpu1(struct lwp *l, void *interlock)
1.8 pooka 440: {
1.1 pooka 441: struct rumpcpu *rcpu;
442: struct cpu_info *ci;
1.15 pooka 443: void *old;
1.1 pooka 444:
445: ci = l->l_cpu;
1.47 ad 446: ci->ci_curlwp = ci->ci_onproc = NULL;
1.43 pooka 447: rcpu = cpuinfo_to_rumpcpu(ci);
1.15 pooka 448:
1.1 pooka 449: KASSERT(rcpu->rcpu_ci == ci);
450:
1.15 pooka 451: /*
452: * Make sure all stores are seen before the CPU release. This
453: * is relevant only in the non-fastpath scheduling case, but
454: * we don't know here if that's going to happen, so need to
455: * expect the worst.
1.29 pooka 456: *
457: * If the scheduler interlock was requested by the caller, we
458: * need to obtain it before we release the CPU. Otherwise, we risk a
459: * race condition where another thread is scheduled onto the
460: * rump kernel CPU before our current thread can
461: * grab the interlock.
1.15 pooka 462: */
1.29 pooka 463: if (interlock == rcpu->rcpu_mtx)
464: rumpuser_mutex_enter_nowrap(rcpu->rcpu_mtx);
465: else
466: membar_exit();
1.15 pooka 467:
468: /* Release the CPU. */
469: old = atomic_swap_ptr(&rcpu->rcpu_prevlwp, l);
470:
471: /* No waiters? No problems. We're outta here. */
472: if (old == RCPULWP_BUSY) {
473: return;
474: }
475:
476: KASSERT(old == RCPULWP_WANTED);
477:
478: /*
479: * Ok, things weren't so snappy.
480: *
481: * Snailpath: take lock and signal anyone waiting for this CPU.
482: */
1.14 pooka 483:
1.29 pooka 484: if (interlock != rcpu->rcpu_mtx)
485: rumpuser_mutex_enter_nowrap(rcpu->rcpu_mtx);
1.15 pooka 486: if (rcpu->rcpu_wanted)
1.8 pooka 487: rumpuser_cv_broadcast(rcpu->rcpu_cv);
1.29 pooka 488: if (interlock != rcpu->rcpu_mtx)
1.15 pooka 489: rumpuser_mutex_exit(rcpu->rcpu_mtx);
1.1 pooka 490: }
1.5 pooka 491:
492: /* Give up and retake CPU (perhaps a different one) */
493: void
494: yield()
495: {
496: struct lwp *l = curlwp;
497: int nlocks;
498:
499: KERNEL_UNLOCK_ALL(l, &nlocks);
500: rump_unschedule_cpu(l);
501: rump_schedule_cpu(l);
502: KERNEL_LOCK(nlocks, l);
503: }
504:
505: void
506: preempt()
507: {
508:
509: yield();
510: }
1.10 pooka 511:
512: bool
513: kpreempt(uintptr_t where)
514: {
515:
516: return false;
517: }
518:
519: /*
520: * There is no kernel thread preemption in rump currently. But call
521: * the implementing macros anyway in case they grow some side-effects
522: * down the road.
523: */
524: void
525: kpreempt_disable(void)
526: {
527:
1.35 pooka 528: KPREEMPT_DISABLE(curlwp);
1.10 pooka 529: }
530:
531: void
532: kpreempt_enable(void)
533: {
534:
1.35 pooka 535: KPREEMPT_ENABLE(curlwp);
1.10 pooka 536: }
537:
1.38 rmind 538: bool
539: kpreempt_disabled(void)
540: {
1.39 rmind 541: #if 0
1.38 rmind 542: const lwp_t *l = curlwp;
543:
544: return l->l_nopreempt != 0 || l->l_stat == LSZOMB ||
1.39 rmind 545: (l->l_flag & LW_IDLE) != 0 || cpu_kpreempt_disabled();
546: #endif
547: /* XXX: emulate cpu_kpreempt_disabled() */
548: return true;
1.38 rmind 549: }
550:
1.10 pooka 551: void
552: suspendsched(void)
553: {
554:
555: /*
556: * Could wait until everyone is out and block further entries,
557: * but skip that for now.
558: */
559: }
1.11 pooka 560:
561: void
562: sched_nice(struct proc *p, int level)
563: {
564:
565: /* nothing to do for now */
566: }
1.37 pooka 567:
568: void
1.45 ad 569: setrunnable(struct lwp *l)
570: {
571:
572: sched_enqueue(l);
573: }
574:
575: void
576: sched_enqueue(struct lwp *l)
1.37 pooka 577: {
578:
579: rump_thread_allow(l);
580: }
581:
582: void
1.45 ad 583: sched_resched_cpu(struct cpu_info *ci, pri_t pri, bool unlock)
584: {
585:
586: }
587:
588: void
589: sched_resched_lwp(struct lwp *l, bool unlock)
590: {
591:
592: }
593:
594: void
1.37 pooka 595: sched_dequeue(struct lwp *l)
596: {
597:
598: panic("sched_dequeue not implemented");
599: }
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