[PATCH] rcu: add deprecation notice about limit on defer queue element size

[PATCH] rcu: add deprecation notice about limit on defer queue element size

[Andre Muezerie]

The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
no limit on the size of each element in the defer queue. With DPDK 25.11 a
hard limit will be set (``RTE_QSBR_ESIZE_MAX``). This will allow fixed
C arrays to be used in the functions' implementations, avoiding VLAs and
use of alloca().

Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
---
 doc/guides/rel_notes/deprecation.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 36489f6e68..78b2a27b52 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -17,6 +17,12 @@ Other API and ABI deprecation notices are to be posted below.
 Deprecation Notices
 -------------------
 
+* rcu: The functions ``rte_rcu_qsbr_dq_create`` and ``rte_rcu_qsbr_dq_reclaim``
+  establish no limit on the size of each element in the defer queue. With
+  DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``). This will
+  allow fixed C arrays to be used in the functions' implementations,
+  avoiding VLAs and use of alloca().
+
 * build: The ``enable_kmods`` option is deprecated and will be removed in a future release.
   Setting/clearing the option has no impact on the build.
   Instead, kernel modules will be always built for OS's where out-of-tree kernel modules
-- 
2.49.0.vfs.0.3

Re: [PATCH] rcu: add deprecation notice about limit on defer queue element size

[David Marchand]

On Fri, May 23, 2025 at 1:37 AM Andre Muezerie
<andremue@linux.microsoft.com> wrote:
>
> The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
> no limit on the size of each element in the defer queue. With DPDK 25.11 a
> hard limit will be set (``RTE_QSBR_ESIZE_MAX``). This will allow fixed
> C arrays to be used in the functions' implementations, avoiding VLAs and
> use of alloca().
>
> Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>

Acked-by: David Marchand <david.marchand@redhat.com>


-- 
David Marchand

Re: [PATCH] rcu: add deprecation notice about limit on defer queue element size

[Thomas Monjalon]

23/05/2025 01:37, Andre Muezerie:
> The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
> no limit on the size of each element in the defer queue.

Very good, we need more unlimited API in DPDK.

> With DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``).

I think it is a step in the wrong direction.
I prefer having no limit.

> This will allow fixed C arrays to be used in the functions' implementations,
> avoiding VLAs and use of alloca().

I don't understand this justification.
Why trying to remove the 2 alloca() in the lib RCU?