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| author | SeongJae Park <sjpark@amazon.de> | 2020-09-23 09:18:40 +0300 |
|---|---|---|
| committer | Boris Ostrovsky <boris.ostrovsky@oracle.com> | 2020-10-21 15:15:15 +0300 |
| commit | 74a852479c68e4efb3865d5436fd69ec4f819f96 (patch) | |
| tree | f563297238066c0bc69526fabd04f0ead31550fa | |
| parent | aac8a70db24bd3916b9ddce1761e500771356b6b (diff) | |
| download | linux-74a852479c68e4efb3865d5436fd69ec4f819f96.tar.xz | |
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>
| -rw-r--r-- | Documentation/ABI/testing/sysfs-driver-xen-blkfront | 9 | ||||
| -rw-r--r-- | 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..48629d3433b4 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -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); |