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| author | SeongJae Park <sjpark@amazon.de> | 2020-09-23 08:18:39 +0200 |
|---|---|---|
| committer | Boris Ostrovsky <boris.ostrovsky@oracle.com> | 2020-10-21 07:15:13 -0500 |
| commit | aac8a70db24bd3916b9ddce1761e500771356b6b (patch) | |
| tree | 8ee9b85e9dd2fdf536e0a0cc0e591dbbecc00774 | |
| parent | 5f7f77400ab5b357b5fdb7122c3442239672186c (diff) | |
| download | linux-aac8a70db24bd3916b9ddce1761e500771356b6b.tar.gz linux-aac8a70db24bd3916b9ddce1761e500771356b6b.tar.bz2 linux-aac8a70db24bd3916b9ddce1761e500771356b6b.zip | |
xen-blkback: 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. But, there is no option to disable it. For
the reason, this commit adds a module parameter for disabling of the
feature.
[1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
Signed-off-by: Anthony Liguori <aliguori@amazon.com>
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/20200923061841.20531-2-sjpark@amazon.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
| -rw-r--r-- | Documentation/ABI/testing/sysfs-driver-xen-blkback | 9 | ||||
| -rw-r--r-- | drivers/block/xen-blkback/xenbus.c | 22 |
2 files changed, 25 insertions, 6 deletions
diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback index ecb7942ff146..ac2947b98950 100644 --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback @@ -35,3 +35,12 @@ Description: controls the duration in milliseconds that blkback will not cache any page not backed by a grant mapping. The default is 10ms. + +What: /sys/module/xen_blkback/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 backends. + The default is Y (enable). diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 5e7c36d73dc6..f5705569e2a7 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -473,6 +473,12 @@ static void xen_vbd_free(struct xen_vbd *vbd) vbd->bdev = NULL; } +/* 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"); + static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, unsigned major, unsigned minor, int readonly, int cdrom) @@ -518,6 +524,8 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, if (q && blk_queue_secure_erase(q)) vbd->discard_secure = true; + vbd->feature_gnt_persistent = feature_persistent; + pr_debug("Successful creation of handle=%04x (dom=%u)\n", handle, blkif->domid); return 0; @@ -905,7 +913,8 @@ again: xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support); - err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1); + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", + be->blkif->vbd.feature_gnt_persistent); if (err) { xenbus_dev_fatal(dev, err, "writing %s/feature-persistent", dev->nodename); @@ -1066,7 +1075,6 @@ static int connect_ring(struct backend_info *be) { struct xenbus_device *dev = be->dev; struct xen_blkif *blkif = be->blkif; - unsigned int pers_grants; char protocol[64] = ""; int err, i; char *xspath; @@ -1092,9 +1100,11 @@ static int connect_ring(struct backend_info *be) xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol); return -ENOSYS; } - pers_grants = xenbus_read_unsigned(dev->otherend, "feature-persistent", - 0); - blkif->vbd.feature_gnt_persistent = pers_grants; + if (blkif->vbd.feature_gnt_persistent) + blkif->vbd.feature_gnt_persistent = + xenbus_read_unsigned(dev->otherend, + "feature-persistent", 0); + blkif->vbd.overflow_max_grants = 0; /* @@ -1117,7 +1127,7 @@ static int connect_ring(struct backend_info *be) pr_info("%s: using %d queues, protocol %d (%s) %s\n", dev->nodename, blkif->nr_rings, blkif->blk_protocol, protocol, - pers_grants ? "persistent grants" : ""); + blkif->vbd.feature_gnt_persistent ? "persistent grants" : ""); ring_page_order = xenbus_read_unsigned(dev->otherend, "ring-page-order", 0); |