Jens Axboe <axboe@xxxxxxxxx> writes:
> Plugging is meant to optimize submission of a string of IOs, if we don't
> have more than 2 being submitted, don't bother setting up a plug.
Is there really that much overhead in blk_{start|finish}_plug?
-Jeff
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> fs/aio.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 522c04864d82..ed6c3914477a 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -69,6 +69,12 @@ struct aio_ring {
> struct io_event io_events[0];
> }; /* 128 bytes + ring size */
>
> +/*
> + * Plugging is meant to work with larger batches of IOs. If we don't
> + * have more than the below, then don't bother setting up a plug.
> + */
> +#define AIO_PLUG_THRESHOLD 2
> +
> #define AIO_RING_PAGES 8
>
> struct kioctx_table {
> @@ -1919,7 +1925,8 @@ SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
> if (nr > ctx->nr_events)
> nr = ctx->nr_events;
>
> - blk_start_plug(&plug);
> + if (nr > AIO_PLUG_THRESHOLD)
> + blk_start_plug(&plug);
> for (i = 0; i < nr; i++) {
> struct iocb __user *user_iocb;
>
> @@ -1932,7 +1939,8 @@ SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
> if (ret)
> break;
> }
> - blk_finish_plug(&plug);
> + if (nr > AIO_PLUG_THRESHOLD)
> + blk_finish_plug(&plug);
>
> percpu_ref_put(&ctx->users);
> return i ? i : ret;
> @@ -1959,7 +1967,8 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
> if (nr > ctx->nr_events)
> nr = ctx->nr_events;
>
> - blk_start_plug(&plug);
> + if (nr > AIO_PLUG_THRESHOLD)
> + blk_start_plug(&plug);
> for (i = 0; i < nr; i++) {
> compat_uptr_t user_iocb;
>
> @@ -1972,7 +1981,8 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
> if (ret)
> break;
> }
> - blk_finish_plug(&plug);
> + if (nr > AIO_PLUG_THRESHOLD)
> + blk_finish_plug(&plug);
>
> percpu_ref_put(&ctx->users);
> return i ? i : ret;
