Messages in this thread Patch in this message | | | From | Ming Lei <> | Subject | [PATCH v5 5/5] block: loop: support DIO & AIO | Date | Tue, 9 Jun 2015 21:49:26 +0800 |
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There are about 3 advantages to use direct I/O and AIO on read/write loop's backing file:
1) double cache can be avoided, then memory usage gets decreased a lot
2) not like user space direct I/O, there isn't cost of pinning pages
3) avoid context switch for obtaining good throughput - in buffered file read, random I/O top throughput is often obtained only if they are submitted concurrently from lots of tasks; but for sequential I/O, most of times they can be hit from page cache, so concurrent submissions often introduce unnecessary context switch and can't improve throughput much. There was such discussion[1] to use non-blocking I/O to improve the problem for application. - with direct I/O and AIO, concurrent submissions can be avoided and random read throughput can't be affected meantime
Follows my fio test result:
1. 16 jobs fio test inside ext4 file system over loop block 1) How to run - linux kernel: 4.1.0-rc2-next-20150506 with the patchset - the loop block is over one image on HDD. - linux psync, 16 jobs, size 400M, ext4 over loop block - test result: IOPS from fio output
2) Throughput result: ------------------------------------------------------------- test cases |randread |read |randwrite |write | ------------------------------------------------------------- base |240 |8705 |3763 |20914 ------------------------------------------------------------- base+loop aio |242 |9258 |4577 |21451 -------------------------------------------------------------
3) context switch - context switch decreased by ~16% with loop aio for randread, and decreased by ~33% for read
4) memory usage - After these four tests with loop aio: ~10% memory becomes used - After these four tests without loop aio: more than 55% memory becomes used
2. single job fio test inside ext4 file system over loop block(for Maxim Patlasov) 1) How to run - linux kernel: 4.1.0-rc2-next-20150506 with the patchset - the loop block is over one image on HDD. - linux psync, 1 job, size 4000M, ext4 over loop block - test result: IOPS from fio output
2) Throughput result: ------------------------------------------------------------- test cases |randread |read |randwrite |write | ------------------------------------------------------------- base |109 |21180 |4192 |22782 ------------------------------------------------------------- base+loop aio |114 |21018 |5404 |22670 -------------------------------------------------------------
3) context switch - context switch decreased by ~10% with loop aio for randread, and decreased by ~50% for read
4) memory usage - After these four tests with loop aio: ~10% memory becomes used - After these four tests without loop aio: more than 55% memory becomes used
Both 'context switch' and 'memory usage' data are got from sar.
[1] https://lwn.net/Articles/612483/ [2] sar graph when running fio over loop without the patchset http://kernel.ubuntu.com/~ming/block/loop-aio/v3/lo-nonaio.pdf
[3] sar graph when running fio over loop with the patchset http://kernel.ubuntu.com/~ming/block/loop-aio/v3/lo-aio.pdf
[4] sar graph when running fio over loop without the patchset http://kernel.ubuntu.com/~ming/block/loop-aio/v3/lo-nonaio-1job.pdf
[5] sar graph when running fio over loop with the patchset http://kernel.ubuntu.com/~ming/block/loop-aio/v3/lo-aio-1job.pdf
Signed-off-by: Ming Lei <ming.lei@canonical.com> --- drivers/block/loop.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++--- drivers/block/loop.h | 2 ++ 2 files changed, 71 insertions(+), 3 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 0b1ee2b..9c557d3 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -388,6 +388,65 @@ static int lo_req_flush(struct loop_device *lo, struct request *rq) return ret; } +static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2) +{ + struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb); + struct request *rq = cmd->rq; + + if (ret > 0) + ret = 0; + else if (ret < 0) + ret = -EIO; + + rq->errors = ret; + blk_mq_complete_request(rq); +} + +static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, + loff_t pos, bool rw) +{ + struct iov_iter iter; + struct bio_vec *bvec; + struct bio *bio = cmd->rq->bio; + struct file *file = lo->lo_backing_file; + int ret; + + /* nomerge for loop request queue */ + WARN_ON(cmd->rq->bio != cmd->rq->biotail); + + bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); + iov_iter_bvec(&iter, ITER_BVEC | rw, bvec, + bio_segments(bio), blk_rq_bytes(cmd->rq)); + + cmd->iocb.ki_pos = pos; + cmd->iocb.ki_filp = file; + cmd->iocb.ki_complete = lo_rw_aio_complete; + cmd->iocb.ki_flags = IOCB_DIRECT; + + if (rw == WRITE) + ret = file->f_op->write_iter(&cmd->iocb, &iter); + else + ret = file->f_op->read_iter(&cmd->iocb, &iter); + + if (ret != -EIOCBQUEUED) + cmd->iocb.ki_complete(&cmd->iocb, ret, 0); + return 0; +} + + +static inline int lo_rw_simple(struct loop_device *lo, + struct request *rq, loff_t pos, bool rw) +{ + struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq); + + if (cmd->use_aio) + return lo_rw_aio(lo, cmd, pos, rw); + + if (rw == WRITE) + return lo_write_simple(lo, rq, pos); + else + return lo_read_simple(lo, rq, pos); +} static int do_req_filebacked(struct loop_device *lo, struct request *rq) { @@ -404,13 +463,13 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq) else if (lo->transfer) ret = lo_write_transfer(lo, rq, pos); else - ret = lo_write_simple(lo, rq, pos); + ret = lo_rw_simple(lo, rq, pos, WRITE); } else { if (lo->transfer) ret = lo_read_transfer(lo, rq, pos); else - ret = lo_read_simple(lo, rq, pos); + ret = lo_rw_simple(lo, rq, pos, READ); } return ret; @@ -1550,6 +1609,12 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx, if (lo->lo_state != Lo_bound) return -EIO; + if (lo->use_dio && !lo->transfer && + !(cmd->rq->cmd_flags & (REQ_FLUSH | REQ_DISCARD))) + cmd->use_aio = true; + else + cmd->use_aio = false; + queue_kthread_work(&lo->worker, &cmd->work); return BLK_MQ_RQ_QUEUE_OK; @@ -1569,7 +1634,8 @@ static void loop_handle_cmd(struct loop_cmd *cmd) failed: if (ret) cmd->rq->errors = -EIO; - blk_mq_complete_request(cmd->rq); + if (!cmd->use_aio || ret) + blk_mq_complete_request(cmd->rq); } static void loop_queue_work(struct kthread_work *work) diff --git a/drivers/block/loop.h b/drivers/block/loop.h index d1de221..fb2237c 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -69,6 +69,8 @@ struct loop_cmd { struct kthread_work work; struct request *rq; struct list_head list; + bool use_aio; /* use AIO interface to handle I/O */ + struct kiocb iocb; }; /* Support for loadable transfer modules */ -- 1.9.1
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