mtd: fix a huge latency problem in the MTD CFI and LPDDR flash drivers.
The use of a memcpy() during a spinlock operation will cause very long
thread context switch delays if the flash chip bandwidth is low and the
data to be copied large, because a spinlock will disable preemption.
For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
which request sometimes 128 KiB (the flash erase size), a preemption delay of
20 milliseconds. High priority threads will not be served during this
time, regardless whether this threads access the flash or not. This behavior
breaks real time.
The patch changes all the use of spin_lock operations for xxxx->mutex
into mutex operations, which is exact what the name says and means.
I have checked the code of the drivers and there is no use of atomic
pathes like interrupt or timers. The mtdoops facility will also not be used
by this drivers. So it is dave to replace the spin_lock against mutex.
There is no performance regression since the mutex is normally not
acquired.
Changelog:
06.03.2010 First release
26.03.2010 Fix mutex[1] issue and tested it for compile failure
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/lpddr/lpddr_cmds.c b/drivers/mtd/lpddr/lpddr_cmds.c
index e22ca49..eb6f437 100644
--- a/drivers/mtd/lpddr/lpddr_cmds.c
+++ b/drivers/mtd/lpddr/lpddr_cmds.c
@@ -106,8 +106,7 @@
/* those should be reset too since
they create memory references. */
init_waitqueue_head(&chip->wq);
- spin_lock_init(&chip->_spinlock);
- chip->mutex = &chip->_spinlock;
+ mutex_init(&chip->mutex);
chip++;
}
}
@@ -143,7 +142,7 @@
}
/* OK Still waiting. Drop the lock, wait a while and retry. */
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
if (sleep_time >= 1000000/HZ) {
/*
* Half of the normal delay still remaining
@@ -158,17 +157,17 @@
cond_resched();
timeo--;
}
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
while (chip->state != chip_state) {
/* Someone's suspended the operation: sleep */
DECLARE_WAITQUEUE(wait, current);
set_current_state(TASK_UNINTERRUPTIBLE);
add_wait_queue(&chip->wq, &wait);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
schedule();
remove_wait_queue(&chip->wq, &wait);
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
}
if (chip->erase_suspended || chip->write_suspended) {
/* Suspend has occured while sleep: reset timeout */
@@ -229,20 +228,20 @@
* it'll happily send us to sleep. In any case, when
* get_chip returns success we're clear to go ahead.
*/
- ret = spin_trylock(contender->mutex);
+ ret = mutex_trylock(&contender->mutex);
spin_unlock(&shared->lock);
if (!ret)
goto retry;
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
ret = chip_ready(map, contender, mode);
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
if (ret == -EAGAIN) {
- spin_unlock(contender->mutex);
+ mutex_unlock(&contender->mutex);
goto retry;
}
if (ret) {
- spin_unlock(contender->mutex);
+ mutex_unlock(&contender->mutex);
return ret;
}
spin_lock(&shared->lock);
@@ -251,10 +250,10 @@
* state. Put contender and retry. */
if (chip->state == FL_SYNCING) {
put_chip(map, contender);
- spin_unlock(contender->mutex);
+ mutex_unlock(&contender->mutex);
goto retry;
}
- spin_unlock(contender->mutex);
+ mutex_unlock(&contender->mutex);
}
/* Check if we have suspended erase on this chip.
@@ -264,10 +263,10 @@
spin_unlock(&shared->lock);
set_current_state(TASK_UNINTERRUPTIBLE);
add_wait_queue(&chip->wq, &wait);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
schedule();
remove_wait_queue(&chip->wq, &wait);
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
goto retry;
}
@@ -336,10 +335,10 @@
sleep:
set_current_state(TASK_UNINTERRUPTIBLE);
add_wait_queue(&chip->wq, &wait);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
schedule();
remove_wait_queue(&chip->wq, &wait);
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
return -EAGAIN;
}
}
@@ -355,12 +354,12 @@
if (shared->writing && shared->writing != chip) {
/* give back the ownership */
struct flchip *loaner = shared->writing;
- spin_lock(loaner->mutex);
+ mutex_lock(&loaner->mutex);
spin_unlock(&shared->lock);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
put_chip(map, loaner);
- spin_lock(chip->mutex);
- spin_unlock(loaner->mutex);
+ mutex_lock(&chip->mutex);
+ mutex_unlock(&loaner->mutex);
wake_up(&chip->wq);
return;
}
@@ -413,10 +412,10 @@
wbufsize = 1 << lpddr->qinfo->BufSizeShift;
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_WRITING);
if (ret) {
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
/* Figure out the number of words to write */
@@ -477,7 +476,7 @@
}
out: put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -489,10 +488,10 @@
struct flchip *chip = &lpddr->chips[chipnum];
int ret;
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_ERASING);
if (ret) {
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
send_pfow_command(map, LPDDR_BLOCK_ERASE, adr, 0, NULL);
@@ -504,7 +503,7 @@
goto out;
}
out: put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -517,10 +516,10 @@
struct flchip *chip = &lpddr->chips[chipnum];
int ret = 0;
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_READY);
if (ret) {
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -528,7 +527,7 @@
*retlen = len;
put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -568,9 +567,9 @@
else
thislen = len;
/* get the chip */
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_POINT);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
if (ret)
break;
@@ -610,7 +609,7 @@
else
thislen = len;
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
if (chip->state == FL_POINT) {
chip->ref_point_counter--;
if (chip->ref_point_counter == 0)
@@ -620,7 +619,7 @@
"pointed region\n", map->name);
put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
len -= thislen;
ofs = 0;
@@ -726,10 +725,10 @@
int chipnum = adr >> lpddr->chipshift;
struct flchip *chip = &lpddr->chips[chipnum];
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_LOCKING);
if (ret) {
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -749,7 +748,7 @@
goto out;
}
out: put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -770,10 +769,10 @@
int chipnum = adr >> lpddr->chipshift;
struct flchip *chip = &lpddr->chips[chipnum];
- spin_lock(chip->mutex);
+ mutex_lock(&chip->mutex);
ret = get_chip(map, chip, FL_WRITING);
if (ret) {
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}
@@ -787,7 +786,7 @@
}
out: put_chip(map, chip);
- spin_unlock(chip->mutex);
+ mutex_unlock(&chip->mutex);
return ret;
}