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

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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>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20200923061841.20531-3-sjpark@amazon.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
This commit is contained in:
SeongJae Park 2020-09-23 08:18:40 +02:00 committed by Boris Ostrovsky
parent aac8a70db2
commit 74a852479c
2 changed files with 24 additions and 5 deletions
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9
Documentation/ABI/testing/sysfs-driver-xen-blkfront
View File

@ -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).

20
drivers/block/xen-blkfront.c
View File

@ -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);
@ -2316,9 +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);