Hanna Czenczek <hre...@redhat.com> writes:
> FUSE allows creating multiple request queues by "cloning" /dev/fuse FDs
> (via open("/dev/fuse") + ioctl(FUSE_DEV_IOC_CLONE)).
>
> We can use this to implement multi-threading.
>
> Note that the interface presented here differs from the multi-queue
> interface of virtio-blk: The latter maps virtqueues to iothreads, which
> allows processing multiple virtqueues in a single iothread. The
> equivalent (processing multiple FDs in a single iothread) would not make
> sense for FUSE because those FDs are used in a round-robin fashion by
> the FUSE kernel driver. Putting two of them into a single iothread will
> just create a bottleneck.
>
> Therefore, all we need is an array of iothreads, and we will create one
> "queue" (FD) per thread.
[...]
> Signed-off-by: Hanna Czenczek <hre...@redhat.com>
> ---
> qapi/block-export.json | 8 +-
> block/export/fuse.c | 214 +++++++++++++++++++++++++++++++++--------
> 2 files changed, 179 insertions(+), 43 deletions(-)
>
> diff --git a/qapi/block-export.json b/qapi/block-export.json
> index c783e01a53..0bdd5992eb 100644
> --- a/qapi/block-export.json
> +++ b/qapi/block-export.json
> @@ -179,12 +179,18 @@
> # mount the export with allow_other, and if that fails, try again
> # without. (since 6.1; default: auto)
> #
> +# @iothreads: Enables multi-threading: Handle requests in each of the
> +# given iothreads (instead of the block device's iothread, or the
> +# export's "main" iothread).
When does "the block device's iothread" apply, and when "the export's
main iothread"? Is this something the QMP user needs to know?
> +# For this, the FUSE FD is duplicated so
> +# there is one FD per iothread. (since 10.1)
Is the file descriptor duplication something the QMP user needs to know?
> +#
> # Since: 6.0
> ##
> { 'struct': 'BlockExportOptionsFuse',
> 'data': { 'mountpoint': 'str',
> '*growable': 'bool',
> - '*allow-other': 'FuseExportAllowOther' },
> + '*allow-other': 'FuseExportAllowOther',
> + '*iothreads': ['str'] },
> 'if': 'CONFIG_FUSE' }
>
> ##
[...]
