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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 09-09-2010, 10:07 PM
Mike Snitzer
 
Default dm: use cpu_relax when busy waiting for condition

Switch busy loops from using msleep(1) to cpu_relax().

Any improvement is negligible given the rare nature of these busy wait
conditions -- but cpu_relax() is considered the more polite method to
use for busy loops.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
drivers/md/dm-snap.c | 6 +++---
drivers/md/dm-table.c | 2 +-
drivers/md/dm.c | 2 +-
3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index eed2101..d1f44c1 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -264,12 +264,12 @@ static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)

/*
* This conflicting I/O is extremely improbable in the caller,
- * so msleep(1) is sufficient and there is no need for a wait queue.
+ * so cpu_relax() is sufficient and there is no need for a wait queue.
*/
static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
{
while (__chunk_is_tracked(s, chunk))
- msleep(1);
+ cpu_relax();
}

/*
@@ -1302,7 +1302,7 @@ static void snapshot_dtr(struct dm_target *ti)
unregister_snapshot(s);

while (atomic_read(&s->pending_exceptions_count))
- msleep(1);
+ cpu_relax();
/*
* Ensure instructions in mempool_destroy aren't reordered
* before atomic_read.
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index f9fc07d..2955d46 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -245,7 +245,7 @@ void dm_table_destroy(struct dm_table *t)
return;

while (atomic_read(&t->holders))
- msleep(1);
+ cpu_relax();
smp_mb();

/* free the indexes */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f934e98..4e699e4 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2228,7 +2228,7 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
*/
if (wait)
while (atomic_read(&md->holders))
- msleep(1);
+ cpu_relax();
else if (atomic_read(&md->holders))
DMWARN("%s: Forcibly removing mapped_device still in use! (%d users)",
dm_device_name(md), atomic_read(&md->holders));

--
dm-devel mailing list
dm-devel@redhat.com
https://www.redhat.com/mailman/listinfo/dm-devel
 

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