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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: 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>
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@ -8,3 +8,12 @@ Description:
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is 32 - higher value means more potential throughput but more
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memory usage. The backend picks the minimum of the frontend
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and its default backend value.
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What: /sys/module/xen_blkfront/parameters/feature_persistent
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Date: September 2020
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KernelVersion: 5.10
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Contact: SeongJae Park <sjpark@amazon.de>
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Description:
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Whether to enable the persistent grants feature or not. Note
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that this option only takes effect on newly created frontends.
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The default is Y (enable).
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@ -1866,8 +1866,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
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message = "writing protocol";
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goto abort_transaction;
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}
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err = xenbus_printf(xbt, dev->nodename,
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"feature-persistent", "%u", 1);
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err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
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info->feature_persistent);
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if (err)
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dev_warn(&dev->dev,
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"writing persistent grants feature to xenbus");
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@ -1941,6 +1941,13 @@ static int negotiate_mq(struct blkfront_info *info)
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}
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return 0;
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}
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/* Enable the persistent grants feature. */
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static bool feature_persistent = true;
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module_param(feature_persistent, bool, 0644);
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MODULE_PARM_DESC(feature_persistent,
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"Enables the persistent grants feature");
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/**
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* Entry point to this code when a new device is created. Allocate the basic
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* structures and the ring buffer for communication with the backend, and
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@ -2007,6 +2014,8 @@ static int blkfront_probe(struct xenbus_device *dev,
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info->vdevice = vdevice;
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info->connected = BLKIF_STATE_DISCONNECTED;
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info->feature_persistent = feature_persistent;
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/* Front end dir is a number, which is used as the id. */
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info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
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dev_set_drvdata(&dev->dev, info);
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@ -2316,9 +2325,10 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
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if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
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blkfront_setup_discard(info);
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info->feature_persistent =
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!!xenbus_read_unsigned(info->xbdev->otherend,
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"feature-persistent", 0);
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if (info->feature_persistent)
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info->feature_persistent =
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!!xenbus_read_unsigned(info->xbdev->otherend,
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"feature-persistent", 0);
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indirect_segments = xenbus_read_unsigned(info->xbdev->otherend,
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"feature-max-indirect-segments", 0);
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