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Subject[PATCH] staging: lustre: avoid going through unlock/lock overhead
Date
Unlocking a spin lock and then immediately locking without doing
anything useful in between buys us nothing, except wasting CPU cycles.

Also code size gets smaller.

Before:

text data bss dec hex filename
70415 2356 4108 76879 12c4f drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.o

After:

text data bss dec hex filename
70095 2356 4108 76559 12b0f drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.o

Signed-off-by: Cihangir Akturk <cakturk@gmail.com>
---
drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c b/drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c
index 64763aa..5d9cd33 100644
--- a/drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c
+++ b/drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c
@@ -1624,8 +1624,9 @@ int kiblnd_fmr_pool_map(struct kib_fmr_poolset *fps, struct kib_tx *tx,
__u64 version;
int rc;

- again:
+again:
spin_lock(&fps->fps_lock);
+again_locked:
version = fps->fps_version;
list_for_each_entry(fpo, &fps->fps_pool_list, fpo_list) {
fpo->fpo_deadline = cfs_time_shift(IBLND_POOL_DEADLINE);
@@ -1722,10 +1723,8 @@ int kiblnd_fmr_pool_map(struct kib_fmr_poolset *fps, struct kib_tx *tx,
}

/* EAGAIN and ... */
- if (version != fps->fps_version) {
- spin_unlock(&fps->fps_lock);
- goto again;
- }
+ if (version != fps->fps_version)
+ goto again_locked;
}

if (fps->fps_increasing) {
@@ -1754,9 +1753,8 @@ int kiblnd_fmr_pool_map(struct kib_fmr_poolset *fps, struct kib_tx *tx,
} else {
fps->fps_next_retry = cfs_time_shift(IBLND_POOL_RETRY);
}
- spin_unlock(&fps->fps_lock);

- goto again;
+ goto again_locked;
}

static void kiblnd_fini_pool(struct kib_pool *pool)
@@ -1901,8 +1899,9 @@ struct list_head *kiblnd_pool_alloc_node(struct kib_poolset *ps)
unsigned int trips = 0;
int rc;

- again:
+again:
spin_lock(&ps->ps_lock);
+again_locked:
list_for_each_entry(pool, &ps->ps_pool_list, po_list) {
if (list_empty(&pool->po_free_list))
continue;
@@ -1960,9 +1959,8 @@ struct list_head *kiblnd_pool_alloc_node(struct kib_poolset *ps)
CERROR("Can't allocate new %s pool because out of memory\n",
ps->ps_name);
}
- spin_unlock(&ps->ps_lock);

- goto again;
+ goto again_locked;
}

static void kiblnd_destroy_tx_pool(struct kib_pool *pool)
--
2.7.4
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