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SubjectRe: [PATCH] xen-blkback: add a parameter for disabling of persistent grants
Date
On Tue, 22 Sep 2020 09:18:05 +0200 "Jürgen Groß" <jgross@suse.com> wrote:

> 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.

Oops, I will.

>
> > +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.

Indeed. I will fix these as you recommended in the next spin.


Thanks,
SeongJae Park

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