//
// Cforall Version 1.0.0 Copyright (C) 2019 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// ready_queue.cfa --
//
// Author           : Thierry Delisle
// Created On       : Mon Nov dd 16:29:18 2019
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#define __cforall_thread__
#define _GNU_SOURCE

// #define __CFA_DEBUG_PRINT_READY_QUEUE__


#define USE_RELAXED_FIFO
// #define USE_WORK_STEALING
// #define USE_CPU_WORK_STEALING

#include "bits/defs.hfa"
#include "device/cpu.hfa"
#include "kernel_private.hfa"

#include "stdlib.hfa"
#include "math.hfa"

#include <errno.h>
#include <unistd.h>

extern "C" {
	#include <sys/syscall.h>  // __NR_xxx
}

#include "ready_subqueue.hfa"

static const size_t cache_line_size = 64;

#if !defined(__CFA_NO_STATISTICS__)
	#define __STATS(...) __VA_ARGS__
#else
	#define __STATS(...)
#endif

// No overriden function, no environment variable, no define
// fall back to a magic number
#ifndef __CFA_MAX_PROCESSORS__
	#define __CFA_MAX_PROCESSORS__ 1024
#endif

#if   defined(USE_CPU_WORK_STEALING)
	#define READYQ_SHARD_FACTOR 2
#elif defined(USE_RELAXED_FIFO)
	#define BIAS 4
	#define READYQ_SHARD_FACTOR 4
	#define SEQUENTIAL_SHARD 1
#elif defined(USE_WORK_STEALING)
	#define READYQ_SHARD_FACTOR 2
	#define SEQUENTIAL_SHARD 2
#else
	#error no scheduling strategy selected
#endif

static inline struct thread$ * try_pop(struct cluster * cltr, unsigned w __STATS(, __stats_readyQ_pop_t & stats));
static inline struct thread$ * try_pop(struct cluster * cltr, unsigned i, unsigned j __STATS(, __stats_readyQ_pop_t & stats));
static inline struct thread$ * search(struct cluster * cltr);
static inline [unsigned, bool] idx_from_r(unsigned r, unsigned preferred);


// returns the maximum number of processors the RWLock support
__attribute__((weak)) unsigned __max_processors() {
	const char * max_cores_s = getenv("CFA_MAX_PROCESSORS");
	if(!max_cores_s) {
		__cfadbg_print_nolock(ready_queue, "No CFA_MAX_PROCESSORS in ENV\n");
		return __CFA_MAX_PROCESSORS__;
	}

	char * endptr = 0p;
	long int max_cores_l = strtol(max_cores_s, &endptr, 10);
	if(max_cores_l < 1 || max_cores_l > 65535) {
		__cfadbg_print_nolock(ready_queue, "CFA_MAX_PROCESSORS out of range : %ld\n", max_cores_l);
		return __CFA_MAX_PROCESSORS__;
	}
	if('\0' != *endptr) {
		__cfadbg_print_nolock(ready_queue, "CFA_MAX_PROCESSORS not a decimal number : %s\n", max_cores_s);
		return __CFA_MAX_PROCESSORS__;
	}

	return max_cores_l;
}

#if   defined(CFA_HAVE_LINUX_LIBRSEQ)
	// No forward declaration needed
	#define __kernel_rseq_register rseq_register_current_thread
	#define __kernel_rseq_unregister rseq_unregister_current_thread
#elif defined(CFA_HAVE_LINUX_RSEQ_H)
	void __kernel_raw_rseq_register  (void);
	void __kernel_raw_rseq_unregister(void);

	#define __kernel_rseq_register __kernel_raw_rseq_register
	#define __kernel_rseq_unregister __kernel_raw_rseq_unregister
#else
	// No forward declaration needed
	// No initialization needed
	static inline void noop(void) {}

	#define __kernel_rseq_register noop
	#define __kernel_rseq_unregister noop
#endif

//=======================================================================
// Cluster wide reader-writer lock
//=======================================================================
void  ?{}(__scheduler_RWLock_t & this) {
	this.max   = __max_processors();
	this.alloc = 0;
	this.ready = 0;
	this.data  = alloc(this.max);
	this.write_lock  = false;

	/*paranoid*/ verify(__atomic_is_lock_free(sizeof(this.alloc), &this.alloc));
	/*paranoid*/ verify(__atomic_is_lock_free(sizeof(this.ready), &this.ready));

}
void ^?{}(__scheduler_RWLock_t & this) {
	free(this.data);
}


//=======================================================================
// Lock-Free registering/unregistering of threads
unsigned register_proc_id( void ) with(*__scheduler_lock) {
	__kernel_rseq_register();

	__cfadbg_print_safe(ready_queue, "Kernel : Registering proc %p for RW-Lock\n", proc);
	bool * handle = (bool *)&kernelTLS().sched_lock;

	// Step - 1 : check if there is already space in the data
	uint_fast32_t s = ready;

	// Check among all the ready
	for(uint_fast32_t i = 0; i < s; i++) {
		bool * volatile * cell = (bool * volatile *)&data[i]; // Cforall is bugged and the double volatiles causes problems
		/* paranoid */ verify( handle != *cell );

		bool * null = 0p; // Re-write every loop since compare thrashes it
		if( __atomic_load_n(cell, (int)__ATOMIC_RELAXED) == null
			&& __atomic_compare_exchange_n( cell, &null, handle, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) {
			/* paranoid */ verify(i < ready);
			/* paranoid */ verify( (kernelTLS().sched_id = i, true) );
			return i;
		}
	}

	if(max <= alloc) abort("Trying to create more than %ud processors", __scheduler_lock->max);

	// Step - 2 : F&A to get a new spot in the array.
	uint_fast32_t n = __atomic_fetch_add(&alloc, 1, __ATOMIC_SEQ_CST);
	if(max <= n) abort("Trying to create more than %ud processors", __scheduler_lock->max);

	// Step - 3 : Mark space as used and then publish it.
	data[n] = handle;
	while() {
		unsigned copy = n;
		if( __atomic_load_n(&ready, __ATOMIC_RELAXED) == n
			&& __atomic_compare_exchange_n(&ready, &copy, n + 1, true, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
			break;
		Pause();
	}

	__cfadbg_print_safe(ready_queue, "Kernel : Registering proc %p done, id %lu\n", proc, n);

	// Return new spot.
	/* paranoid */ verify(n < ready);
	/* paranoid */ verify( (kernelTLS().sched_id = n, true) );
	return n;
}

void unregister_proc_id( unsigned id ) with(*__scheduler_lock) {
	/* paranoid */ verify(id < ready);
	/* paranoid */ verify(id == kernelTLS().sched_id);
	/* paranoid */ verify(data[id] == &kernelTLS().sched_lock);

	bool * volatile * cell = (bool * volatile *)&data[id]; // Cforall is bugged and the double volatiles causes problems

	__atomic_store_n(cell, 0p, __ATOMIC_RELEASE);

	__cfadbg_print_safe(ready_queue, "Kernel : Unregister proc %p\n", proc);

	__kernel_rseq_unregister();
}

//-----------------------------------------------------------------------
// Writer side : acquire when changing the ready queue, e.g. adding more
//  queues or removing them.
uint_fast32_t ready_mutate_lock( void ) with(*__scheduler_lock) {
	/* paranoid */ verify( ! __preemption_enabled() );
	/* paranoid */ verify( ! kernelTLS().sched_lock );

	// Step 1 : lock global lock
	// It is needed to avoid processors that register mid Critical-Section
	//   to simply lock their own lock and enter.
	__atomic_acquire( &write_lock );

	// Step 2 : lock per-proc lock
	// Processors that are currently being registered aren't counted
	//   but can't be in read_lock or in the critical section.
	// All other processors are counted
	uint_fast32_t s = ready;
	for(uint_fast32_t i = 0; i < s; i++) {
		volatile bool * llock = data[i];
		if(llock) __atomic_acquire( llock );
	}

	/* paranoid */ verify( ! __preemption_enabled() );
	return s;
}

void ready_mutate_unlock( uint_fast32_t last_s ) with(*__scheduler_lock) {
	/* paranoid */ verify( ! __preemption_enabled() );

	// Step 1 : release local locks
	// This must be done while the global lock is held to avoid
	//   threads that where created mid critical section
	//   to race to lock their local locks and have the writer
	//   immidiately unlock them
	// Alternative solution : return s in write_lock and pass it to write_unlock
	for(uint_fast32_t i = 0; i < last_s; i++) {
		volatile bool * llock = data[i];
		if(llock) __atomic_store_n(llock, (bool)false, __ATOMIC_RELEASE);
	}

	// Step 2 : release global lock
	/*paranoid*/ assert(true == write_lock);
	__atomic_store_n(&write_lock, (bool)false, __ATOMIC_RELEASE);

	/* paranoid */ verify( ! __preemption_enabled() );
}

//=======================================================================
// Cforall Ready Queue used for scheduling
//=======================================================================
void ?{}(__ready_queue_t & this) with (this) {
	#if defined(USE_CPU_WORK_STEALING)
		lanes.count = cpu_info.hthrd_count * READYQ_SHARD_FACTOR;
		lanes.data = alloc( lanes.count );
		lanes.tscs = alloc( lanes.count );

		for( idx; (size_t)lanes.count ) {
			(lanes.data[idx]){};
			lanes.tscs[idx].tv = rdtscl();
		}
	#else
		lanes.data  = 0p;
		lanes.tscs  = 0p;
		lanes.count = 0;
	#endif
}

void ^?{}(__ready_queue_t & this) with (this) {
	#if !defined(USE_CPU_WORK_STEALING)
		verify( SEQUENTIAL_SHARD == lanes.count );
	#endif

	free(lanes.data);
	free(lanes.tscs);
}

//-----------------------------------------------------------------------
#if defined(USE_CPU_WORK_STEALING)
	__attribute__((hot)) void push(struct cluster * cltr, struct thread$ * thrd, bool push_local) with (cltr->ready_queue) {
		__cfadbg_print_safe(ready_queue, "Kernel : Pushing %p on cluster %p\n", thrd, cltr);

		processor * const proc = kernelTLS().this_processor;
		const bool external = !push_local || (!proc) || (cltr != proc->cltr);

		const int cpu = __kernel_getcpu();
		/* paranoid */ verify(cpu >= 0);
		/* paranoid */ verify(cpu < cpu_info.hthrd_count);
		/* paranoid */ verify(cpu * READYQ_SHARD_FACTOR < lanes.count);

		const cpu_map_entry_t & map = cpu_info.llc_map[cpu];
		/* paranoid */ verify(map.start * READYQ_SHARD_FACTOR < lanes.count);
		/* paranoid */ verify(map.self * READYQ_SHARD_FACTOR < lanes.count);
		/* paranoid */ verifyf((map.start + map.count) * READYQ_SHARD_FACTOR <= lanes.count, "have %zu lanes but map can go up to %u", lanes.count, (map.start + map.count) * READYQ_SHARD_FACTOR);

		const int start = map.self * READYQ_SHARD_FACTOR;
		unsigned i;
		do {
			unsigned r;
			if(unlikely(external)) { r = __tls_rand(); }
			else { r = proc->rdq.its++; }
			i = start + (r % READYQ_SHARD_FACTOR);
			// If we can't lock it retry
		} while( !__atomic_try_acquire( &lanes.data[i].lock ) );

		// Actually push it
		push(lanes.data[i], thrd);

		// Unlock and return
		__atomic_unlock( &lanes.data[i].lock );

		#if !defined(__CFA_NO_STATISTICS__)
			if(unlikely(external)) __atomic_fetch_add(&cltr->stats->ready.push.extrn.success, 1, __ATOMIC_RELAXED);
			else __tls_stats()->ready.push.local.success++;
		#endif

		__cfadbg_print_safe(ready_queue, "Kernel : Pushed %p on cluster %p (idx: %u, mask %llu, first %d)\n", thrd, cltr, i, used.mask[0], lane_first);

	}

	// Pop from the ready queue from a given cluster
	__attribute__((hot)) thread$ * pop_fast(struct cluster * cltr) with (cltr->ready_queue) {
		/* paranoid */ verify( lanes.count > 0 );
		/* paranoid */ verify( kernelTLS().this_processor );

		const int cpu = __kernel_getcpu();
		/* paranoid */ verify(cpu >= 0);
		/* paranoid */ verify(cpu < cpu_info.hthrd_count);
		/* paranoid */ verify(cpu * READYQ_SHARD_FACTOR < lanes.count);

		const cpu_map_entry_t & map = cpu_info.llc_map[cpu];
		/* paranoid */ verify(map.start * READYQ_SHARD_FACTOR < lanes.count);
		/* paranoid */ verify(map.self * READYQ_SHARD_FACTOR < lanes.count);
		/* paranoid */ verifyf((map.start + map.count) * READYQ_SHARD_FACTOR <= lanes.count, "have %zu lanes but map can go up to %u", lanes.count, (map.start + map.count) * READYQ_SHARD_FACTOR);

		processor * const proc = kernelTLS().this_processor;
		const int start = map.self * READYQ_SHARD_FACTOR;

		// Did we already have a help target
		if(proc->rdq.target == -1u) {
			// if We don't have a
			unsigned long long min = ts(lanes.data[start]);
			for(i; READYQ_SHARD_FACTOR) {
				unsigned long long tsc = ts(lanes.data[start + i]);
				if(tsc < min) min = tsc;
			}
			proc->rdq.cutoff = min;

			/* paranoid */ verify(lanes.count < 65536); // The following code assumes max 65536 cores.
			/* paranoid */ verify(map.count < 65536); // The following code assumes max 65536 cores.

			if(0 == (__tls_rand() % 10_000)) {
				proc->rdq.target = __tls_rand() % lanes.count;
			} else {
				unsigned cpu_chaos = map.start + (__tls_rand() % map.count);
				proc->rdq.target = (cpu_chaos * READYQ_SHARD_FACTOR) + (__tls_rand() % READYQ_SHARD_FACTOR);
				/* paranoid */ verify(proc->rdq.target >= (map.start * READYQ_SHARD_FACTOR));
				/* paranoid */ verify(proc->rdq.target <  ((map.start + map.count) * READYQ_SHARD_FACTOR));
			}

			/* paranoid */ verify(proc->rdq.target != -1u);
		}
		else {
			const unsigned long long bias = 0; //2_500_000_000;
			const unsigned long long cutoff = proc->rdq.cutoff > bias ? proc->rdq.cutoff - bias : proc->rdq.cutoff;
			{
				unsigned target = proc->rdq.target;
				proc->rdq.target = -1u;
				if(lanes.tscs[target].tv < cutoff && ts(lanes.data[target]) < cutoff) {
					thread$ * t = try_pop(cltr, target __STATS(, __tls_stats()->ready.pop.help));
					proc->rdq.last = target;
					if(t) return t;
				}
			}

			unsigned last = proc->rdq.last;
			if(last != -1u && lanes.tscs[last].tv < cutoff && ts(lanes.data[last]) < cutoff) {
				thread$ * t = try_pop(cltr, last __STATS(, __tls_stats()->ready.pop.help));
				if(t) return t;
			}
			else {
				proc->rdq.last = -1u;
			}
		}

		for(READYQ_SHARD_FACTOR) {
			unsigned i = start + (proc->rdq.itr++ % READYQ_SHARD_FACTOR);
			if(thread$ * t = try_pop(cltr, i __STATS(, __tls_stats()->ready.pop.local))) return t;
		}

		// All lanes where empty return 0p
		return 0p;
	}

	__attribute__((hot)) struct thread$ * pop_slow(struct cluster * cltr) with (cltr->ready_queue) {
		processor * const proc = kernelTLS().this_processor;
		unsigned last = proc->rdq.last;
		if(last != -1u) {
			struct thread$ * t = try_pop(cltr, last __STATS(, __tls_stats()->ready.pop.steal));
			if(t) return t;
			proc->rdq.last = -1u;
		}

		unsigned i = __tls_rand() % lanes.count;
		return try_pop(cltr, i __STATS(, __tls_stats()->ready.pop.steal));
	}
	__attribute__((hot)) struct thread$ * pop_search(struct cluster * cltr) {
		return search(cltr);
	}
#endif
#if defined(USE_RELAXED_FIFO)
	//-----------------------------------------------------------------------
	// get index from random number with or without bias towards queues
	static inline [unsigned, bool] idx_from_r(unsigned r, unsigned preferred) {
		unsigned i;
		bool local;
		unsigned rlow  = r % BIAS;
		unsigned rhigh = r / BIAS;
		if((0 != rlow) && preferred >= 0) {
			// (BIAS - 1) out of BIAS chances
			// Use perferred queues
			i = preferred + (rhigh % READYQ_SHARD_FACTOR);
			local = true;
		}
		else {
			// 1 out of BIAS chances
			// Use all queues
			i = rhigh;
			local = false;
		}
		return [i, local];
	}

	__attribute__((hot)) void push(struct cluster * cltr, struct thread$ * thrd, bool push_local) with (cltr->ready_queue) {
		__cfadbg_print_safe(ready_queue, "Kernel : Pushing %p on cluster %p\n", thrd, cltr);

		const bool external = !push_local || (!kernelTLS().this_processor) || (cltr != kernelTLS().this_processor->cltr);
		/* paranoid */ verify(external || kernelTLS().this_processor->rdq.id < lanes.count );

		bool local;
		int preferred = external ? -1 : kernelTLS().this_processor->rdq.id;

		// Try to pick a lane and lock it
		unsigned i;
		do {
			// Pick the index of a lane
			unsigned r = __tls_rand_fwd();
			[i, local] = idx_from_r(r, preferred);

			i %= __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );

			#if !defined(__CFA_NO_STATISTICS__)
				if(unlikely(external)) __atomic_fetch_add(&cltr->stats->ready.push.extrn.attempt, 1, __ATOMIC_RELAXED);
				else if(local) __tls_stats()->ready.push.local.attempt++;
				else __tls_stats()->ready.push.share.attempt++;
			#endif

			// If we can't lock it retry
		} while( !__atomic_try_acquire( &lanes.data[i].lock ) );

		// Actually push it
		push(lanes.data[i], thrd);

		// Unlock and return
		__atomic_unlock( &lanes.data[i].lock );

		// Mark the current index in the tls rng instance as having an item
		__tls_rand_advance_bck();

		__cfadbg_print_safe(ready_queue, "Kernel : Pushed %p on cluster %p (idx: %u, mask %llu, first %d)\n", thrd, cltr, i, used.mask[0], lane_first);

		// Update statistics
		#if !defined(__CFA_NO_STATISTICS__)
			if(unlikely(external)) __atomic_fetch_add(&cltr->stats->ready.push.extrn.success, 1, __ATOMIC_RELAXED);
			else if(local) __tls_stats()->ready.push.local.success++;
			else __tls_stats()->ready.push.share.success++;
		#endif
	}

	// Pop from the ready queue from a given cluster
	__attribute__((hot)) thread$ * pop_fast(struct cluster * cltr) with (cltr->ready_queue) {
		/* paranoid */ verify( lanes.count > 0 );
		/* paranoid */ verify( kernelTLS().this_processor );
		/* paranoid */ verify( kernelTLS().this_processor->rdq.id < lanes.count );

		unsigned count = __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );
		int preferred = kernelTLS().this_processor->rdq.id;


		// As long as the list is not empty, try finding a lane that isn't empty and pop from it
		for(25) {
			// Pick two lists at random
			unsigned ri = __tls_rand_bck();
			unsigned rj = __tls_rand_bck();

			unsigned i, j;
			__attribute__((unused)) bool locali, localj;
			[i, locali] = idx_from_r(ri, preferred);
			[j, localj] = idx_from_r(rj, preferred);

			i %= count;
			j %= count;

			// try popping from the 2 picked lists
			struct thread$ * thrd = try_pop(cltr, i, j __STATS(, *(locali || localj ? &__tls_stats()->ready.pop.local : &__tls_stats()->ready.pop.help)));
			if(thrd) {
				return thrd;
			}
		}

		// All lanes where empty return 0p
		return 0p;
	}

	__attribute__((hot)) struct thread$ * pop_slow(struct cluster * cltr) { return pop_fast(cltr); }
	__attribute__((hot)) struct thread$ * pop_search(struct cluster * cltr) {
		return search(cltr);
	}
#endif
#if defined(USE_WORK_STEALING)
	__attribute__((hot)) void push(struct cluster * cltr, struct thread$ * thrd, bool push_local) with (cltr->ready_queue) {
		__cfadbg_print_safe(ready_queue, "Kernel : Pushing %p on cluster %p\n", thrd, cltr);

		// #define USE_PREFERRED
		#if !defined(USE_PREFERRED)
		const bool external = !push_local || (!kernelTLS().this_processor) || (cltr != kernelTLS().this_processor->cltr);
		/* paranoid */ verify(external || kernelTLS().this_processor->rdq.id < lanes.count );
		#else
			unsigned preferred = thrd->preferred;
			const bool external = push_local || (!kernelTLS().this_processor) || preferred == -1u || thrd->curr_cluster != cltr;
			/* paranoid */ verifyf(external || preferred < lanes.count, "Invalid preferred queue %u for %u lanes", preferred, lanes.count );

			unsigned r = preferred % READYQ_SHARD_FACTOR;
			const unsigned start = preferred - r;
		#endif

		// Try to pick a lane and lock it
		unsigned i;
		do {
			#if !defined(__CFA_NO_STATISTICS__)
				if(unlikely(external)) __atomic_fetch_add(&cltr->stats->ready.push.extrn.attempt, 1, __ATOMIC_RELAXED);
				else __tls_stats()->ready.push.local.attempt++;
			#endif

			if(unlikely(external)) {
				i = __tls_rand() % lanes.count;
			}
			else {
				#if !defined(USE_PREFERRED)
					processor * proc = kernelTLS().this_processor;
					unsigned r = proc->rdq.its++;
					i =  proc->rdq.id + (r % READYQ_SHARD_FACTOR);
				#else
					i = start + (r++ % READYQ_SHARD_FACTOR);
				#endif
			}
			// If we can't lock it retry
		} while( !__atomic_try_acquire( &lanes.data[i].lock ) );

		// Actually push it
		push(lanes.data[i], thrd);

		// Unlock and return
		__atomic_unlock( &lanes.data[i].lock );

		#if !defined(__CFA_NO_STATISTICS__)
			if(unlikely(external)) __atomic_fetch_add(&cltr->stats->ready.push.extrn.success, 1, __ATOMIC_RELAXED);
			else __tls_stats()->ready.push.local.success++;
		#endif

		__cfadbg_print_safe(ready_queue, "Kernel : Pushed %p on cluster %p (idx: %u, mask %llu, first %d)\n", thrd, cltr, i, used.mask[0], lane_first);
	}

	// Pop from the ready queue from a given cluster
	__attribute__((hot)) thread$ * pop_fast(struct cluster * cltr) with (cltr->ready_queue) {
		/* paranoid */ verify( lanes.count > 0 );
		/* paranoid */ verify( kernelTLS().this_processor );
		/* paranoid */ verify( kernelTLS().this_processor->rdq.id < lanes.count );

		processor * proc = kernelTLS().this_processor;

		if(proc->rdq.target == -1u) {
			unsigned long long min = ts(lanes.data[proc->rdq.id]);
			for(int i = 0; i < READYQ_SHARD_FACTOR; i++) {
				unsigned long long tsc = ts(lanes.data[proc->rdq.id + i]);
				if(tsc < min) min = tsc;
			}
			proc->rdq.cutoff = min;
			proc->rdq.target = __tls_rand() % lanes.count;
		}
		else {
			unsigned target = proc->rdq.target;
			proc->rdq.target = -1u;
			const unsigned long long bias = 0; //2_500_000_000;
			const unsigned long long cutoff = proc->rdq.cutoff > bias ? proc->rdq.cutoff - bias : proc->rdq.cutoff;
			if(lanes.tscs[target].tv < cutoff && ts(lanes.data[target]) < cutoff) {
				thread$ * t = try_pop(cltr, target __STATS(, __tls_stats()->ready.pop.help));
				if(t) return t;
			}
		}

		for(READYQ_SHARD_FACTOR) {
			unsigned i = proc->rdq.id + (proc->rdq.itr++ % READYQ_SHARD_FACTOR);
			if(thread$ * t = try_pop(cltr, i __STATS(, __tls_stats()->ready.pop.local))) return t;
		}
		return 0p;
	}

	__attribute__((hot)) struct thread$ * pop_slow(struct cluster * cltr) with (cltr->ready_queue) {
		unsigned i = __tls_rand() % lanes.count;
		return try_pop(cltr, i __STATS(, __tls_stats()->ready.pop.steal));
	}

	__attribute__((hot)) struct thread$ * pop_search(struct cluster * cltr) with (cltr->ready_queue) {
		return search(cltr);
	}
#endif

//=======================================================================
// Various Ready Queue utilities
//=======================================================================
// these function work the same or almost the same
// whether they are using work-stealing or relaxed fifo scheduling

//-----------------------------------------------------------------------
// try to pop from a lane given by index w
static inline struct thread$ * try_pop(struct cluster * cltr, unsigned w __STATS(, __stats_readyQ_pop_t & stats)) with (cltr->ready_queue) {
	__STATS( stats.attempt++; )

	// Get relevant elements locally
	__intrusive_lane_t & lane = lanes.data[w];

	// If list looks empty retry
	if( is_empty(lane) ) {
		return 0p;
	}

	// If we can't get the lock retry
	if( !__atomic_try_acquire(&lane.lock) ) {
		return 0p;
	}

	// If list is empty, unlock and retry
	if( is_empty(lane) ) {
		__atomic_unlock(&lane.lock);
		return 0p;
	}

	// Actually pop the list
	struct thread$ * thrd;
	unsigned long long tsv;
	[thrd, tsv] = pop(lane);

	/* paranoid */ verify(thrd);
	/* paranoid */ verify(tsv);
	/* paranoid */ verify(lane.lock);

	// Unlock and return
	__atomic_unlock(&lane.lock);

	// Update statistics
	__STATS( stats.success++; )

	#if defined(USE_WORK_STEALING)
		lanes.tscs[w].tv = tsv;
	#endif

	thrd->preferred = w;

	// return the popped thread
	return thrd;
}

//-----------------------------------------------------------------------
// try to pop from any lanes making sure you don't miss any threads push
// before the start of the function
static inline struct thread$ * search(struct cluster * cltr) with (cltr->ready_queue) {
	/* paranoid */ verify( lanes.count > 0 );
	unsigned count = __atomic_load_n( &lanes.count, __ATOMIC_RELAXED );
	unsigned offset = __tls_rand();
	for(i; count) {
		unsigned idx = (offset + i) % count;
		struct thread$ * thrd = try_pop(cltr, idx __STATS(, __tls_stats()->ready.pop.search));
		if(thrd) {
			return thrd;
		}
	}

	// All lanes where empty return 0p
	return 0p;
}

//-----------------------------------------------------------------------
// Check that all the intrusive queues in the data structure are still consistent
static void check( __ready_queue_t & q ) with (q) {
	#if defined(__CFA_WITH_VERIFY__)
		{
			for( idx ; lanes.count ) {
				__intrusive_lane_t & sl = lanes.data[idx];
				assert(!lanes.data[idx].lock);

					if(is_empty(sl)) {
						assert( sl.anchor.next == 0p );
						assert( sl.anchor.ts   == -1llu );
						assert( mock_head(sl)  == sl.prev );
					} else {
						assert( sl.anchor.next != 0p );
						assert( sl.anchor.ts   != -1llu );
						assert( mock_head(sl)  != sl.prev );
					}
			}
		}
	#endif
}

//-----------------------------------------------------------------------
// Given 2 indexes, pick the list with the oldest push an try to pop from it
static inline struct thread$ * try_pop(struct cluster * cltr, unsigned i, unsigned j __STATS(, __stats_readyQ_pop_t & stats)) with (cltr->ready_queue) {
	// Pick the bet list
	int w = i;
	if( __builtin_expect(!is_empty(lanes.data[j]), true) ) {
		w = (ts(lanes.data[i]) < ts(lanes.data[j])) ? i : j;
	}

	return try_pop(cltr, w __STATS(, stats));
}

// Call this function of the intrusive list was moved using memcpy
// fixes the list so that the pointers back to anchors aren't left dangling
static inline void fix(__intrusive_lane_t & ll) {
			if(is_empty(ll)) {
				verify(ll.anchor.next == 0p);
				ll.prev = mock_head(ll);
			}
}

static void assign_list(unsigned & value, dlist(processor) & list, unsigned count) {
	processor * it = &list`first;
	for(unsigned i = 0; i < count; i++) {
		/* paranoid */ verifyf( it, "Unexpected null iterator, at index %u of %u\n", i, count);
		it->rdq.id = value;
		it->rdq.target = -1u;
		value += READYQ_SHARD_FACTOR;
		it = &(*it)`next;
	}
}

static void reassign_cltr_id(struct cluster * cltr) {
	unsigned preferred = 0;
	assign_list(preferred, cltr->procs.actives, cltr->procs.total - cltr->procs.idle);
	assign_list(preferred, cltr->procs.idles  , cltr->procs.idle );
}

static void fix_times( struct cluster * cltr ) with( cltr->ready_queue ) {
	#if defined(USE_WORK_STEALING)
		lanes.tscs = alloc(lanes.count, lanes.tscs`realloc);
		for(i; lanes.count) {
			unsigned long long tsc1 = ts(lanes.data[i]);
			unsigned long long tsc2 = rdtscl();
			lanes.tscs[i].tv = min(tsc1, tsc2);
		}
	#endif
}

#if defined(USE_CPU_WORK_STEALING)
	// ready_queue size is fixed in this case
	void ready_queue_grow(struct cluster * cltr) {}
	void ready_queue_shrink(struct cluster * cltr) {}
#else
	// Grow the ready queue
	void ready_queue_grow(struct cluster * cltr) {
		size_t ncount;
		int target = cltr->procs.total;

		/* paranoid */ verify( ready_mutate_islocked() );
		__cfadbg_print_safe(ready_queue, "Kernel : Growing ready queue\n");

		// Make sure that everything is consistent
		/* paranoid */ check( cltr->ready_queue );

		// grow the ready queue
		with( cltr->ready_queue ) {
			// Find new count
			// Make sure we always have atleast 1 list
			if(target >= 2) {
				ncount = target * READYQ_SHARD_FACTOR;
			} else {
				ncount = SEQUENTIAL_SHARD;
			}

			// Allocate new array (uses realloc and memcpies the data)
			lanes.data = alloc( ncount, lanes.data`realloc );

			// Fix the moved data
			for( idx; (size_t)lanes.count ) {
				fix(lanes.data[idx]);
			}

			// Construct new data
			for( idx; (size_t)lanes.count ~ ncount) {
				(lanes.data[idx]){};
			}

			// Update original
			lanes.count = ncount;
		}

		fix_times(cltr);

		reassign_cltr_id(cltr);

		// Make sure that everything is consistent
		/* paranoid */ check( cltr->ready_queue );

		__cfadbg_print_safe(ready_queue, "Kernel : Growing ready queue done\n");

		/* paranoid */ verify( ready_mutate_islocked() );
	}

	// Shrink the ready queue
	void ready_queue_shrink(struct cluster * cltr) {
		/* paranoid */ verify( ready_mutate_islocked() );
		__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue\n");

		// Make sure that everything is consistent
		/* paranoid */ check( cltr->ready_queue );

		int target = cltr->procs.total;

		with( cltr->ready_queue ) {
			// Remember old count
			size_t ocount = lanes.count;

			// Find new count
			// Make sure we always have atleast 1 list
			lanes.count = target >= 2 ? target * READYQ_SHARD_FACTOR: SEQUENTIAL_SHARD;
			/* paranoid */ verify( ocount >= lanes.count );
			/* paranoid */ verify( lanes.count == target * READYQ_SHARD_FACTOR || target < 2 );

			// for printing count the number of displaced threads
			#if defined(__CFA_DEBUG_PRINT__) || defined(__CFA_DEBUG_PRINT_READY_QUEUE__)
				__attribute__((unused)) size_t displaced = 0;
			#endif

			// redistribute old data
			for( idx; (size_t)lanes.count ~ ocount) {
				// Lock is not strictly needed but makes checking invariants much easier
				__attribute__((unused)) bool locked = __atomic_try_acquire(&lanes.data[idx].lock);
				verify(locked);

				// As long as we can pop from this lane to push the threads somewhere else in the queue
				while(!is_empty(lanes.data[idx])) {
					struct thread$ * thrd;
					unsigned long long _;
					[thrd, _] = pop(lanes.data[idx]);

					push(cltr, thrd, true);

					// for printing count the number of displaced threads
					#if defined(__CFA_DEBUG_PRINT__) || defined(__CFA_DEBUG_PRINT_READY_QUEUE__)
						displaced++;
					#endif
				}

				// Unlock the lane
				__atomic_unlock(&lanes.data[idx].lock);

				// TODO print the queue statistics here

				^(lanes.data[idx]){};
			}

			__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue displaced %zu threads\n", displaced);

			// Allocate new array (uses realloc and memcpies the data)
			lanes.data = alloc( lanes.count, lanes.data`realloc );

			// Fix the moved data
			for( idx; (size_t)lanes.count ) {
				fix(lanes.data[idx]);
			}
		}

		fix_times(cltr);

		reassign_cltr_id(cltr);

		// Make sure that everything is consistent
		/* paranoid */ check( cltr->ready_queue );

		__cfadbg_print_safe(ready_queue, "Kernel : Shrinking ready queue done\n");
		/* paranoid */ verify( ready_mutate_islocked() );
	}
#endif

#if !defined(__CFA_NO_STATISTICS__)
	unsigned cnt(const __ready_queue_t & this, unsigned idx) {
		/* paranoid */ verify(this.lanes.count > idx);
		return this.lanes.data[idx].cnt;
	}
#endif


#if   defined(CFA_HAVE_LINUX_LIBRSEQ)
	// No definition needed
#elif defined(CFA_HAVE_LINUX_RSEQ_H)

	#if defined( __x86_64 ) || defined( __i386 )
		#define RSEQ_SIG	0x53053053
	#elif defined( __ARM_ARCH )
		#ifdef __ARMEB__
		#define RSEQ_SIG    0xf3def5e7      /* udf    #24035    ; 0x5de3 (ARMv6+) */
		#else
		#define RSEQ_SIG    0xe7f5def3      /* udf    #24035    ; 0x5de3 */
		#endif
	#endif

	extern void __disable_interrupts_hard();
	extern void __enable_interrupts_hard();

	void __kernel_raw_rseq_register  (void) {
		/* paranoid */ verify( __cfaabi_rseq.cpu_id == RSEQ_CPU_ID_UNINITIALIZED );

		// int ret = syscall(__NR_rseq, &__cfaabi_rseq, sizeof(struct rseq), 0, (sigset_t *)0p, _NSIG / 8);
		int ret = syscall(__NR_rseq, &__cfaabi_rseq, sizeof(struct rseq), 0, RSEQ_SIG);
		if(ret != 0) {
			int e = errno;
			switch(e) {
			case EINVAL: abort("KERNEL ERROR: rseq register invalid argument");
			case ENOSYS: abort("KERNEL ERROR: rseq register no supported");
			case EFAULT: abort("KERNEL ERROR: rseq register with invalid argument");
			case EBUSY : abort("KERNEL ERROR: rseq register already registered");
			case EPERM : abort("KERNEL ERROR: rseq register sig  argument  on unregistration does not match the signature received on registration");
			default: abort("KERNEL ERROR: rseq register unexpected return %d", e);
			}
		}
	}

	void __kernel_raw_rseq_unregister(void) {
		/* paranoid */ verify( __cfaabi_rseq.cpu_id >= 0 );

		// int ret = syscall(__NR_rseq, &__cfaabi_rseq, sizeof(struct rseq), RSEQ_FLAG_UNREGISTER, (sigset_t *)0p, _NSIG / 8);
		int ret = syscall(__NR_rseq, &__cfaabi_rseq, sizeof(struct rseq), RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
		if(ret != 0) {
			int e = errno;
			switch(e) {
			case EINVAL: abort("KERNEL ERROR: rseq unregister invalid argument");
			case ENOSYS: abort("KERNEL ERROR: rseq unregister no supported");
			case EFAULT: abort("KERNEL ERROR: rseq unregister with invalid argument");
			case EBUSY : abort("KERNEL ERROR: rseq unregister already registered");
			case EPERM : abort("KERNEL ERROR: rseq unregister sig  argument  on unregistration does not match the signature received on registration");
			default: abort("KERNEL ERROR: rseq unregisteunexpected return %d", e);
			}
		}
	}
#else
	// No definition needed
#endif