doc: add limitation on MPRQ usage in multi-process app
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Commit Message
MPRQ cannot be used in multi-process applications because of
externally attached MPRQ buffers. A callback is registered by
a primary process to free MPRQ buffers once they are no longer
needed. But this information is shared among all the processes.
The virtual address of the mlx5_mprq_buf_free_cb function is
different in a secondary process, which leads to a segmentation
fault. Document that MPRQ is not supported in a multi-process
app, since there is no way to find out if this is the one.
Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---
doc/guides/nics/mlx5.rst | 3 +++
1 file changed, 3 insertions(+)
Comments
Hi,
> -----Original Message-----
> From: Alexander Kozyrev <akozyrev@nvidia.com>
> Sent: Friday, February 4, 2022 5:19 AM
> To: dev@dpdk.org
> Cc: Raslan Darawsheh <rasland@nvidia.com>; Slava Ovsiienko
> <viacheslavo@nvidia.com>; Matan Azrad <matan@nvidia.com>
> Subject: [PATCH] doc: add limitation on MPRQ usage in multi-process app
>
> MPRQ cannot be used in multi-process applications because of
> externally attached MPRQ buffers. A callback is registered by
> a primary process to free MPRQ buffers once they are no longer
> needed. But this information is shared among all the processes.
> The virtual address of the mlx5_mprq_buf_free_cb function is
> different in a secondary process, which leads to a segmentation
> fault. Document that MPRQ is not supported in a multi-process
> app, since there is no way to find out if this is the one.
>
> Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
> Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Patch applied to next-net-mlx,
Kindest regards,
Raslan Darawsheh
@@ -138,6 +138,9 @@ Limitations
- For secondary process:
- Forked secondary process not supported.
+ - MPRQ is not supported. Callback to free externally attached MPRQ buffer is sets
+ in a primary process, but has a different virtual address in a secondary process.
+ Calling a function at the wrong address leads to a segmentation fault.
- External memory unregistered in EAL memseg list cannot be used for DMA
unless such memory has been registered by ``mlx5_mr_update_ext_mp()`` in
primary process and remapped to the same virtual address in secondary