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SubjectRe: [PATCH v3 2/3] xen-blkfront: add a parameter for disabling of persistent grants
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On Tue, 22 Sep 2020 16:27:03 +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. It can be disabled from blkback side using a
> > module parameter, 'feature_persistent'. But, it is impossible from
> > blkfront side. For the reason, this commit adds a blkfront module
> > parameter for disabling of the feature.
> >
> > [1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
> >
> > Signed-off-by: SeongJae Park <sjpark@amazon.de>
> > ---
> > .../ABI/testing/sysfs-driver-xen-blkfront | 9 +++++++++
> > drivers/block/xen-blkfront.c | 20 ++++++++++++++-----
> > 2 files changed, 24 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
> > index c0a6cb7eb314..9c31334cb2e6 100644
> > --- a/Documentation/ABI/testing/sysfs-driver-xen-blkfront
> > +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
> > @@ -8,3 +8,12 @@ Description:
> > is 32 - higher value means more potential throughput but more
> > memory usage. The backend picks the minimum of the frontend
> > and its default backend value.
> > +
> > +What: /sys/module/xen_blkfront/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 frontends.
> > + The default is Y (enable).
> > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > index 91de2e0755ae..b2d3b1262404 100644
> > --- a/drivers/block/xen-blkfront.c
> > +++ b/drivers/block/xen-blkfront.c
> > @@ -1866,8 +1866,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
> > message = "writing protocol";
> > goto abort_transaction;
> > }
> > - err = xenbus_printf(xbt, dev->nodename,
> > - "feature-persistent", "%u", 1);
> > + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
> > + info->feature_persistent);
> > if (err)
> > dev_warn(&dev->dev,
> > "writing persistent grants feature to xenbus");
> > @@ -1941,6 +1941,13 @@ static int negotiate_mq(struct blkfront_info *info)
> > }
> > return 0;
> > }
> > +
> > +/* 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");
> > +
> > /**
> > * Entry point to this code when a new device is created. Allocate the basic
> > * structures and the ring buffer for communication with the backend, and
> > @@ -2007,6 +2014,8 @@ static int blkfront_probe(struct xenbus_device *dev,
> > info->vdevice = vdevice;
> > info->connected = BLKIF_STATE_DISCONNECTED;
> >
> > + info->feature_persistent = feature_persistent ? 1 : 0;
>
> Just use the value.

Yes, I will.

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

Appreciate :)


Thanks,
SeongJae Park

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