Document for users that FUSE's multi-threading implementation
distributes requests in a round-robin manner, regardless of where they
originate from.

As noted by Stefan, this will probably change with a FUSE-over-io_uring
implementation (which is supposed to have CPU affinity), but documenting
that is left for once that is done.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
---
 qapi/block-export.json | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/qapi/block-export.json b/qapi/block-export.json
index ee30606680..9ae703ad01 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -163,6 +163,11 @@
 # Options for exporting a block graph node on some (file) mountpoint
 # as a raw image.
 #
+# Multi-threading note: The FUSE export supports multi-threading.
+# Currently, requests are distributed across these threads in a
+# round-robin fashion, i.e. independently of the CPU core from which a
+# request originates.
+#
 # @mountpoint: Path on which to export the block device via FUSE.
 #     This must point to an existing regular file.
 #
-- 
2.49.0

On Tue, Jul 01, 2025 at 01:44:35PM +0200, Hanna Czenczek wrote:
> Document for users that FUSE's multi-threading implementation
> distributes requests in a round-robin manner, regardless of where they
> originate from.
> 
> As noted by Stefan, this will probably change with a FUSE-over-io_uring
> implementation (which is supposed to have CPU affinity), but documenting
> that is left for once that is done.
> 
> Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Acked-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
> ---
>  qapi/block-export.json | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>