From: SeongJae Park <[email protected]>
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 <[email protected]>
---
.../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 <[email protected]>
+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;
+
/* Front end dir is a number, which is used as the id. */
info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
dev_set_drvdata(&dev->dev, info);
@@ -2316,9 +2325,10 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
blkfront_setup_discard(info);
- info->feature_persistent =
- !!xenbus_read_unsigned(info->xbdev->otherend,
- "feature-persistent", 0);
+ if (info->feature_persistent)
+ info->feature_persistent =
+ !!xenbus_read_unsigned(info->xbdev->otherend,
+ "feature-persistent", 0);
indirect_segments = xenbus_read_unsigned(info->xbdev->otherend,
"feature-max-indirect-segments", 0);
--
2.17.1
On 22.09.20 16:15, SeongJae Park wrote:
> From: SeongJae Park <[email protected]>
>
> 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 <[email protected]>
> ---
> .../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 <[email protected]>
> +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.
With that changed:
Reviewed-by: Juergen Gross <[email protected]>
Juergen
On Tue, 22 Sep 2020 16:27:03 +0200 "Jürgen Groß" <[email protected]> wrote:
> On 22.09.20 16:15, SeongJae Park wrote:
> > From: SeongJae Park <[email protected]>
> >
> > 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 <[email protected]>
> > ---
> > .../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 <[email protected]>
> > +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 <[email protected]>
Appreciate :)
Thanks,
SeongJae Park