Re: [Qemu-devel] [PATCH v2 2/2] block: bump coroutine pool size for drives

[Markus Armbruster]

Stefan Hajnoczi <address@hidden> writes:

> When a BlockDriverState is associated with a storage controller
> DeviceState we expect guest I/O.  Use this opportunity to bump the
> coroutine pool size by 64.
>
> This patch ensures that the coroutine pool size scales with the number
> of drives attached to the guest.  It should increase coroutine pool
> usage (which makes qemu_coroutine_create() fast) without hogging too
> much memory when fewer drives are attached.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  block.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/block.c b/block.c
> index f80e2b2..c8379ca 100644
> --- a/block.c
> +++ b/block.c
> @@ -2093,6 +2093,9 @@ int bdrv_attach_dev(BlockDriverState *bs, void *dev)
>      }
>      bs->dev = dev;
>      bdrv_iostatus_reset(bs);
> +
> +    /* We're expecting I/O from the device so bump up coroutine pool size */
> +    qemu_coroutine_adjust_pool_size(64);
>      return 0;
>  }
>  
> @@ -2112,6 +2115,7 @@ void bdrv_detach_dev(BlockDriverState *bs, void *dev)
>      bs->dev_ops = NULL;
>      bs->dev_opaque = NULL;
>      bs->guest_block_size = 512;
> +    qemu_coroutine_adjust_pool_size(-64);
>  }
>  
>  /* TODO change to return DeviceState * when all users are qdevified */

This enlarges the pool regardless of how the device model uses the block
layer.  Isn't this a bit crude?

Have you considered adapting the number of coroutines to actual demand?
Within reasonable limits, of course.