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SubjectRe: [PATCH v3 1/3] xen-blkback: add a parameter for disabling of persistent grants
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On Tue, 22 Sep 2020 16:25:57 +0200 "Jürgen Groß" <jgross@suse.com> wrote:

> 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?

I will do so in the next version.

>
> With that changed you can add my
>
> Reviewed-by: Juergen Gross <jgross@suse.com>

Thank you for your kind, quick, and detailed review!


Thanks,
SeongJae Park

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