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SubjectRe: [PATCH v3 1/3] xen-blkback: add a parameter for disabling of persistent grants
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On 22.09.20 16:15, 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 overheads[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 | 9 ++++++++
> drivers/block/xen-blkback/xenbus.c | 22 ++++++++++++++-----
> 2 files changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> index ecb7942ff146..ac2947b98950 100644
> --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
> +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> @@ -35,3 +35,12 @@ 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. Note
> + that this option only takes effect on newly created backends.
> + The default is Y (enable).
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index b9aa5d1ac10b..f4c8827fa0ad 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -474,6 +474,12 @@ static void xen_vbd_free(struct xen_vbd *vbd)
> vbd->bdev = NULL;
> }
>
> +/* Enable the persistent grants feature. */
> +static bool feature_persistent = true;
> +module_param(feature_persistent, bool, 0644);
> +MODULE_PARM_DESC(feature_persistent,
> + "Enables the persistent grants feature");
> +
> static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
> unsigned major, unsigned minor, int readonly,
> int cdrom)
> @@ -519,6 +525,8 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
> if (q && blk_queue_secure_erase(q))
> vbd->discard_secure = true;
>
> + vbd->feature_gnt_persistent = feature_persistent ? 1 : 0;

Just assign the value instead of using the ternary operator?

With that changed you can add my

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen

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