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blk-mq: switch ctx pending map to the sparser blk_align_bitmap

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Each hardware queue has a bitmap of software queues with pending
requests. When new IO is queued on a software queue, the bit is
set, and when IO is pruned on a hardware queue run, the bit is
cleared. This causes a lot of traffic. Switch this from the regular
BITS_PER_LONG bitmap to a sparser layout, similarly to what was
done for blk-mq tagging.

20% performance increase was observed for single threaded IO, and
about 15% performanc increase on multiple threads driving the
same device.

Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Jens Axboe 2014-05-19 09:23:55 -06:00
parent e93ecf602b
commit 1429d7c946
2 changed files with 99 additions and 30 deletions
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10
include/linux/blk-mq.h
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@ -11,6 +11,12 @@ struct blk_mq_cpu_notifier {
void (*notify)(void *data, unsigned long action, unsigned int cpu);
};
struct blk_mq_ctxmap {
unsigned int map_size;
unsigned int bits_per_word;
struct blk_align_bitmap *map;
};
struct blk_mq_hw_ctx {
struct {
spinlock_t lock;
@ -31,8 +37,8 @@ struct blk_mq_hw_ctx {
void *driver_data;
unsigned int nr_ctx_map;
unsigned long *ctx_map;
struct blk_mq_ctxmap ctx_map;
unsigned int nr_ctx;
struct blk_mq_ctx **ctxs;