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.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

diff --git a/fs/aio.c b/fs/aio.c
index e29ec485af255822b8414be128fc8ef66da9a204..75e05c91605d4a85193533d2f82dca7e814ee3ed 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1622,7 +1622,6 @@ 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;
@@ -1639,8 +1638,6 @@ 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?
@@ -1663,7 +1660,6 @@ 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;