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Subject[PATCH] AIO: Don't plug the I/O queue in do_io_submit()
Asynchronous I/O latency to a solid-state disk greatly increased
between the 2.6.32 and 3.0 kernels. By removing the plug from
do_io_submit(), we observed a 34% improvement in the I/O latency.

Unfortunately, at this level, we don't know if the request is to
a rotating disk or not.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: linux-aio@kvack.org
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>

diff --git a/fs/aio.c b/fs/aio.c
index 78c514c..d131a2c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1696,7 +1696,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,
struct kioctx *ctx;
long ret = 0;
int i = 0;
- struct blk_plug plug;
struct kiocb_batch batch;

if (unlikely(nr < 0))
@@ -1716,8 +1715,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,

kiocb_batch_init(&batch, nr);

- blk_start_plug(&plug);
-
/*
* AKPM: should this return a partial result if some of the IOs were
* successfully submitted?
@@ -1740,7 +1737,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,
if (ret)
break;
}
- blk_finish_plug(&plug);

kiocb_batch_free(&batch);
put_ioctx(ctx);

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