On Tue, Jan 11, 2022 at 06:19:50PM +0900, Hiroki Narukawa wrote:
> Coroutine pool size was 64 from long ago, and the basis was organized in the
> commit message in c740ad92.
>
> At that time, virtio-blk queue-size and num-queue were not configuable, and
> equivalent values were 128 and 1.
>
> Coroutine pool size 64 was fine then.
>
> Later queue-size and num-queue got configuable, and default values were
> increased.
>
> Coroutine pool with size 64 exhausts frequently with random disk IO in new
> size, and slows down.
>
> This commit adjusts coroutine pool size adaptively with new values.
>
> This commit adds 64 by default, but now coroutine is not only for block
> devices,
>
> and is not too much burdon comparing with new default.
>
> pool size of 128 * vCPUs.
>
> Signed-off-by: Hiroki Narukawa <hnaru...@yahoo-corp.jp>
> ---
> hw/block/virtio-blk.c | 3 +++
> include/qemu/coroutine.h | 5 +++++
> util/qemu-coroutine.c | 15 +++++++++++----
> 3 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index f139cd7cc9..726dbe14de 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -32,6 +32,7 @@
> #include "hw/virtio/virtio-bus.h"
> #include "migration/qemu-file-types.h"
> #include "hw/virtio/virtio-access.h"
> +#include "qemu/coroutine.h"
>
> /* Config size before the discard support (hide associated config fields) */
> #define VIRTIO_BLK_CFG_SIZE offsetof(struct virtio_blk_config, \
> @@ -1222,6 +1223,8 @@ static void virtio_blk_device_realize(DeviceState *dev,
> Error **errp)
> for (i = 0; i < conf->num_queues; i++) {
> virtio_add_queue(vdev, conf->queue_size, virtio_blk_handle_output);
> }
> + qemu_coroutine_increase_pool_batch_size(conf->num_queues *
> conf->queue_size
> + / 2);
Why "/ 2"?
> virtio_blk_data_plane_create(vdev, conf, &s->dataplane, &err);
> if (err != NULL) {
> error_propagate(errp, err);
Please handle hot unplug (->unrealize()) so the coroutine pool shrinks
down again when virtio-blk devices are removed.
My main concern is memory footprint. A burst of I/O can create many
coroutines and they might never be used again. But I think we can deal
with that using a timer in a separate future patch (if necessary).
Thanks,
Stefan
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