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* [PATCH] vhost: restrict set max queue pair API to VDUSE
@ 2024-10-02 14:42 Maxime Coquelin
  2024-10-03  6:47 ` David Marchand
  0 siblings, 1 reply; 2+ messages in thread
From: Maxime Coquelin @ 2024-10-02 14:42 UTC (permalink / raw)
  To: dev, chenbox, david.marchand; +Cc: stable, yux.jiang, Maxime Coquelin

In order to avoid breaking Vhost-user live-migration, we want the
rte_vhost_driver_set_max_queue_num API to only be effective with
VDUSE.

Furthermore, this API is only really needed for VDUSE where the
device number of queues is defined by the backend. For Vhost-user,
this is defined by the frontend (e.g. QEMU), so the advantages of
restricting more the maximum number of queue pairs is limited to
a small memory gain (a handful of pointers).

Fixes: 4aa1f88ac13d ("vhost: add API to set max queue pairs")
Cc: stable@dpdk.org

Reported-by: Yu Jiang <yux.jiang@intel.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/socket.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/vhost/socket.c b/lib/vhost/socket.c
index a75728a2e4..d29d15494c 100644
--- a/lib/vhost/socket.c
+++ b/lib/vhost/socket.c
@@ -860,6 +860,18 @@ rte_vhost_driver_set_max_queue_num(const char *path, uint32_t max_queue_pairs)
 		goto unlock_exit;
 	}
 
+	/*
+	 * This is only useful for VDUSE for which number of virtqueues is set
+	 * by the backend. For Vhost-user, the number of virtqueues is defined
+	 * by the frontend.
+	 */
+	if (!vsocket->is_vduse) {
+		VHOST_CONFIG_LOG(path, DEBUG,
+				"Keeping %u max queue pairs for Vhost-user backend",
+				VHOST_MAX_QUEUE_PAIRS);
+		goto unlock_exit;
+	}
+
 	vsocket->max_queue_pairs = max_queue_pairs;
 
 unlock_exit:
-- 
2.46.1


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] vhost: restrict set max queue pair API to VDUSE
  2024-10-02 14:42 [PATCH] vhost: restrict set max queue pair API to VDUSE Maxime Coquelin
@ 2024-10-03  6:47 ` David Marchand
  0 siblings, 0 replies; 2+ messages in thread
From: David Marchand @ 2024-10-03  6:47 UTC (permalink / raw)
  To: Maxime Coquelin; +Cc: dev, chenbox, stable, yux.jiang

On Wed, Oct 2, 2024 at 4:42 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> In order to avoid breaking Vhost-user live-migration, we want the
> rte_vhost_driver_set_max_queue_num API to only be effective with
> VDUSE.
>
> Furthermore, this API is only really needed for VDUSE where the
> device number of queues is defined by the backend. For Vhost-user,
> this is defined by the frontend (e.g. QEMU), so the advantages of
> restricting more the maximum number of queue pairs is limited to
> a small memory gain (a handful of pointers).
>
> Fixes: 4aa1f88ac13d ("vhost: add API to set max queue pairs")
> Cc: stable@dpdk.org
>
> Reported-by: Yu Jiang <yux.jiang@intel.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Should this be documented in the API?

Otherwise, this looks ok to me.


-- 
David Marchand


^ permalink raw reply	[flat|nested] 2+ messages in thread

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