[PATCH] doc: add information to update dma entry limit

[PATCH] doc: add information to update dma entry limit

[Nipun Gupta]

VFIO module provides configurable dma_entry_limit
parameter to store the DMA entries. By default this
is 64K and if we are using --no-huge, we shall need
to increase the value of dma_entry_limit. Add
commands in linux_gsg document to change the
dma_entry_limit.

Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
---
 doc/guides/linux_gsg/linux_drivers.rst | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
index 2cec1ebede..b729bb38a8 100644
--- a/doc/guides/linux_gsg/linux_drivers.rst
+++ b/doc/guides/linux_gsg/linux_drivers.rst
@@ -180,6 +180,21 @@ VFIO module parameter ``dma_entry_limit`` with a default value of 64K.
 When application is out of DMA entries, these limits need to be adjusted to
 increase the allowed limit.
 
+When ``no-huge`` parameter is used, the page size used is of smaller size of
+``4K`` or ``64K`` and we shall need to increase ``dma_entry_limit``.
+To update the ``dma_entry_limit``, ``vfio_iommu_type1`` has to be loaded with
+additional module parameter:
+
+.. code-block:: console
+
+   modprobe vfio_iommu_type1 dma_entry_limit=512000
+
+Alternatively, one can also change this value in an already loaded kernel module:
+
+.. code-block:: console
+
+   echo 512000 > /sys/module/vfio_iommu_type1/parameters/dma_entry_limit
+
 Creating Virtual Functions using vfio-pci
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.17.1

Re: [PATCH] doc: add information to update dma entry limit

[Thomas Monjalon]

05/07/2023 12:53, Nipun Gupta:
> VFIO module provides configurable dma_entry_limit
> parameter to store the DMA entries. By default this
> is 64K and if we are using --no-huge, we shall need
> to increase the value of dma_entry_limit. Add
> commands in linux_gsg document to change the
> dma_entry_limit.
> 
> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
> ---
>  doc/guides/linux_gsg/linux_drivers.rst | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
> index 2cec1ebede..b729bb38a8 100644
> --- a/doc/guides/linux_gsg/linux_drivers.rst
> +++ b/doc/guides/linux_gsg/linux_drivers.rst
> @@ -180,6 +180,21 @@ VFIO module parameter ``dma_entry_limit`` with a default value of 64K.
>  When application is out of DMA entries, these limits need to be adjusted to
>  increase the allowed limit.
>  
> +When ``no-huge`` parameter is used, the page size used is of smaller size of

I would add "--" to have the full option "--no-huge".
By the way, this is an "option" in the shell language :-)

> +``4K`` or ``64K`` and we shall need to increase ``dma_entry_limit``.
> +To update the ``dma_entry_limit``, ``vfio_iommu_type1`` has to be loaded with
> +additional module parameter:
> +
> +.. code-block:: console
> +
> +   modprobe vfio_iommu_type1 dma_entry_limit=512000
> +
> +Alternatively, one can also change this value in an already loaded kernel module:
> +
> +.. code-block:: console
> +
> +   echo 512000 > /sys/module/vfio_iommu_type1/parameters/dma_entry_limit

That looks good, thank you.

[PATCH v2] doc: add information to update dma entry limit

[Nipun Gupta]

VFIO module provides configurable dma_entry_limit
parameter to store the DMA entries. By default this
is 64K and if we are using --no-huge, we shall need
to increase the value of dma_entry_limit. Add
commands in linux_gsg document to change the
dma_entry_limit.

Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
---

Changes v1->v2:
- updated param 'no-huge' to '--no-huge' in documentation

 doc/guides/linux_gsg/linux_drivers.rst | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
index 2cec1ebede..b729bb38a8 100644
--- a/doc/guides/linux_gsg/linux_drivers.rst
+++ b/doc/guides/linux_gsg/linux_drivers.rst
@@ -180,6 +180,21 @@ VFIO module parameter ``dma_entry_limit`` with a default value of 64K.
 When application is out of DMA entries, these limits need to be adjusted to
 increase the allowed limit.
 
+When ``--no-huge`` parameter is used, the page size used is of smaller size of
+``4K`` or ``64K`` and we shall need to increase ``dma_entry_limit``.
+To update the ``dma_entry_limit``, ``vfio_iommu_type1`` has to be loaded with
+additional module parameter:
+
+.. code-block:: console
+
+   modprobe vfio_iommu_type1 dma_entry_limit=512000
+
+Alternatively, one can also change this value in an already loaded kernel module:
+
+.. code-block:: console
+
+   echo 512000 > /sys/module/vfio_iommu_type1/parameters/dma_entry_limit
+
 Creating Virtual Functions using vfio-pci
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.17.1

Re: [PATCH v2] doc: add information to update dma entry limit

[Thomas Monjalon]

05/07/2023 15:39, Nipun Gupta:
> VFIO module provides configurable dma_entry_limit
> parameter to store the DMA entries. By default this
> is 64K and if we are using --no-huge, we shall need
> to increase the value of dma_entry_limit. Add
> commands in linux_gsg document to change the
> dma_entry_limit.
> 
> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>

Applied, thanks.