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SubjectRe: [PATCH] xen-blkback: add a parameter for disabling of persistent grants
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On 22.09.20 09:01, SeongJae Park wrote:
> From: SeongJae Park <sjpark@amazon.de>
>
> Persistent grants feature provides high scalability. On some small
> systems, however, it could incur data copy overhead[1] and thus it is
> required to be disabled. But, there is no option to disable it. For
> the reason, this commit adds a module parameter for disabling of the
> feature.
>
> [1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
>
> Signed-off-by: Anthony Liguori <aliguori@amazon.com>
> Signed-off-by: SeongJae Park <sjpark@amazon.de>
> ---
> .../ABI/testing/sysfs-driver-xen-blkback | 8 ++++++++
> drivers/block/xen-blkback/xenbus.c | 17 ++++++++++++++---
> 2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> index ecb7942ff146..0c42285c75ee 100644
> --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
> +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> @@ -35,3 +35,11 @@ Description:
> controls the duration in milliseconds that blkback will not
> cache any page not backed by a grant mapping.
> The default is 10ms.
> +
> +What: /sys/module/xen_blkback/parameters/feature_persistent
> +Date: September 2020
> +KernelVersion: 5.10
> +Contact: SeongJae Park <sjpark@amazon.de>
> +Description:
> + Whether to enable the persistent grants feature or not.
> + The default is 1 (enable).
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index b9aa5d1ac10b..9c03d70469f4 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -879,6 +879,12 @@ static void reclaim_memory(struct xenbus_device *dev)
>
> /* ** Connection ** */
>
> +/* Enable the persistent grants feature. */
> +static unsigned int feature_persistent = 1;

Use bool, please.

> +module_param_named(feature_persistent, feature_persistent, int, 0644);

module_param()

> +MODULE_PARM_DESC(feature_persistent,
> + "Enables the persistent grants feature");
> +
> /*
> * Write the physical details regarding the block device to the store, and
> * switch to Connected state.
> @@ -906,7 +912,8 @@ static void connect(struct backend_info *be)
>
> xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
>
> - err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
> + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
> + feature_persistent ? 1 : 0);

Using bool above should allow to just use the value of
feature_persistent here.


Juergen

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