Commit 74a85247 authored by SeongJae Park's avatar SeongJae Park Committed by Boris Ostrovsky
Browse files

xen-blkfront: add a parameter for disabling of persistent grants 

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: default avatarSeongJae Park <sjpark@amazon.de>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Acked-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20200923061841.20531-3-sjpark@amazon.com


Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent aac8a70d

Documentation/ABI/testing/sysfs-driver-xen-blkfront

+9 −0
Original line number Diff line number Diff line
@@ -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).

drivers/block/xen-blkfront.c

+15 −5
Original line number Diff line number Diff line
@@ -1866,8 +1866,8 @@ again: 
		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;



	/* 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);
@@ -2316,6 +2325,7 @@ static void blkfront_gather_backend_features(struct blkfront_info *info) 
	if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))

		blkfront_setup_discard(info);



	if (info->feature_persistent)

		info->feature_persistent =

			!!xenbus_read_unsigned(info->xbdev->otherend,

					       "feature-persistent", 0);

CRA Git | Maintained and supported by SUSTech CRA and CCSE