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/* -*- c++ -*- */
/*
* Copyright 2007,2008,2009 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <gcell/spu/gc_jd_queue.h>
#include <gcell/spu/gc_delay.h>
#include <gcell/spu/gc_random.h>
#include "mutex_lock.h"
#include "mutex_unlock.h"
#define MIN(a,b) ((a) < (b) ? (a) : (b))
extern int gc_sys_tag;
// keep track of stats
int jdq_ok;
int jdq_empty;
int jdq_locked;
#define INITIAL_BACKOFF 32.0
#define MAX_BACKOFF 8192.0 /* 2.6us */
#define RANDOM_WEIGHT 0.2
static float
next_backoff(float backoff)
{
// exponential with random
float t = backoff * 2.0;
if (t > MAX_BACKOFF)
t = MAX_BACKOFF;
float r = (RANDOM_WEIGHT * (2.0 * (gc_uniform_deviate() - 0.5)));
t = t * (1.0 + r);
return t;
}
gc_dequeue_status_t
gc_jd_queue_dequeue(gc_eaddr_t q, gc_eaddr_t *item_ea,
int jd_tag, gc_job_desc_t *item)
{
int status;
char _tmp[256];
gc_jd_queue_t *local_q =
(gc_jd_queue_t *) ALIGN(_tmp, 128); // get cache-aligned buffer
float backoff = next_backoff(INITIAL_BACKOFF);
do {
// Copy the queue structure in and get a lock line reservation.
// (The structure is 128-byte aligned and completely fills a cache-line)
mfc_getllar(local_q, q, 0, 0);
spu_readch(MFC_RdAtomicStat);
if (local_q->mutex != 0){ // somebody else has it locked
jdq_locked++;
return GCQ_LOCKED;
}
if (local_q->head == 0){ // the queue is empty
jdq_empty++;
return GCQ_EMPTY;
}
// Try to acquire the lock
local_q->mutex = 1;
mfc_putllc(local_q, q, 0, 0);
status = spu_readch(MFC_RdAtomicStat);
if (status != 0){
gc_cdelay((int) backoff);
backoff = next_backoff(backoff);
}
} while (status != 0);
// we're now holding the lock
// copy in job descriptor at head of queue
*item_ea = local_q->head;
// We must use the fence with the jd_tag to ensure that any
// previously initiated put of a job desc is locally ordered before
// the get of the new one.
mfc_getf(item, local_q->head, sizeof(gc_job_desc_t), jd_tag, 0, 0);
mfc_write_tag_mask(1 << jd_tag); // the tag we're interested in
mfc_read_tag_status_all(); // wait for DMA to complete
local_q->head = item->sys.next;
item->sys.next = 0;
if (local_q->head == 0) // now empty?
local_q->tail = 0;
// Copy the queue struct back out and unlock the mutex in one fell swoop.
// We use the unconditional put since it's faster and we own the lock.
local_q->mutex = 0;
mfc_putlluc(local_q, q, 0, 0);
spu_readch(MFC_RdAtomicStat);
jdq_ok++;
return GCQ_OK;
}
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