AcoSail/kernel_optimize_test
8
0
Fork 0
forked from luck/tmp_suning_uos_patched
Code Pull Requests Activity

sbitmap: re-initialize allocation hints after resize

Browse Source 
After a struct sbitmap_queue is resized smaller, the allocation hints
may still be set to bits beyond the new depth of the bitmap. This means
that, for example, if the number of blk-mq tags is reduced through
sysfs, more requests than the nominal queue depth may be in flight.

It's tempting to fix this at resize time by doing a one-time
reinitialization of the hints, but this can race with
__sbitmap_queue_get() updating the hint. Instead, check the hint before
we use it. This caused no measurable performance difference in my
synthetic benchmarks.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Omar Sandoval 2016-09-17 01:28:26 -07:00 committed by Jens Axboe
parent 98d95416db
commit 05fd095d53
1 changed files with 7 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
lib/sbitmap.c
View File

@ -246,10 +246,15 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
int __sbitmap_queue_get(struct sbitmap_queue *sbq) int __sbitmap_queue_get(struct sbitmap_queue *sbq)
{ {
unsigned int hint; unsigned int hint, depth;
int nr; int nr;
hint = this_cpu_read(*sbq->alloc_hint); hint = this_cpu_read(*sbq->alloc_hint);
depth = READ_ONCE(sbq->sb.depth);
if (unlikely(hint >= depth)) {
hint = depth ? prandom_u32() % depth : 0;
this_cpu_write(*sbq->alloc_hint, hint);
}
nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin); nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
if (nr == -1) { if (nr == -1) {
@ -258,7 +263,7 @@ int __sbitmap_queue_get(struct sbitmap_queue *sbq)
} else if (nr == hint || unlikely(sbq->round_robin)) { } else if (nr == hint || unlikely(sbq->round_robin)) {
/* Only update the hint if we used it. */ /* Only update the hint if we used it. */
hint = nr + 1; hint = nr + 1;
if (hint >= sbq->sb.depth - 1) if (hint >= depth - 1)
hint = 0; hint = 0;
this_cpu_write(*sbq->alloc_hint, hint); this_cpu_write(*sbq->alloc_hint, hint);
} }