blk-mq: support per-distpatch_queue flush machinery
This patch supports to run one single flush machinery for
each blk-mq dispatch queue, so that:
- current init_request and exit_request callbacks can
cover flush request too, then the buggy copying way of
initializing flush request's pdu can be fixed
- flushing performance gets improved in case of multi hw-queue
In fio sync write test over virtio-blk(4 hw queues, ioengine=sync,
iodepth=64, numjobs=4, bs=4K), it is observed that througput gets
increased a lot over my test environment:
- throughput: +70% in case of virtio-blk over null_blk
- throughput: +30% in case of virtio-blk over SSD image
The multi virtqueue feature isn't merged to QEMU yet, and patches for
the feature can be found in below tree:
git://kernel.ubuntu.com/ming/qemu.git v2.1.0-mq.4
And simply passing 'num_queues=4 vectors=5' should be enough to
enable multi queue(quad queue) feature for QEMU virtio-blk.
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 3253495..02c5d95 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -4,6 +4,7 @@
#include <linux/blkdev.h>
struct blk_mq_tags;
+struct blk_flush_queue;
struct blk_mq_cpu_notifier {
struct list_head list;
@@ -34,6 +35,7 @@
struct request_queue *queue;
unsigned int queue_num;
+ struct blk_flush_queue *fq;
void *driver_data;
@@ -119,6 +121,10 @@
/*
* Called for every command allocated by the block layer to allow
* the driver to set up driver specific data.
+ *
+ * Tag greater than or equal to queue_depth is for setting up
+ * flush request.
+ *
* Ditto for exit/teardown.
*/
init_request_fn *init_request;