Asynchronous I/O latency to a solid-state disk greatly increased betw…

…een 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>
Signed-off-by: umberto1978 <ur.tecnotop@gmail.com>

fs/aio.c

@@ -1618,7 +1618,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,
 	struct kioctx *ctx;
 	long ret = 0;
 	int i;
-	struct blk_plug plug;
 
 	if (unlikely(nr < 0))
 		return -EINVAL;
@@ -1635,8 +1634,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,
 		return -EINVAL;
 	}
 
-	blk_start_plug(&plug);
-
 	/*
 	 * AKPM: should this return a partial result if some of the IOs were
 	 * successfully submitted?
@@ -1659,7 +1656,6 @@ long do_io_submit(aio_context_t ctx_id, long nr,
 		if (ret)
 			break;
 	}
-	blk_finish_plug(&plug);
 
 	put_ioctx(ctx);
 	return i ? i : ret;