From: SeongJae Park <[email protected]>
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 module parameters for disabling of the
feature.
[1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability
Baseline and Complete Git Trees
===============================
The patches are based on the v5.9-rc6. You can also clone the complete
git tree:
$ git clone git://github.com/sjp38/linux -b pgrants_disable_v4
The web is also available:
https://github.com/sjp38/linux/tree/pgrants_disable_v4
Patch History
=============
Changes from v3
(https://lore.kernel.org/xen-devel/[email protected]/)
- Remove unnecessary ternary operation (Jürgen Groß)
- Add 'Reviewed-by: Juergen Gross <[email protected]>' and
'Acked-by: Roger Pau Monné <[email protected]>'
Changes from v2
(https://lore.kernel.org/linux-block/[email protected]/)
- Avoid a race condition (Roger Pau Monné)
Because the option value is written twice, there could be a race if the
user change the value meanwhile. This version fixes the problem by
reading the value once when each (front|back)end is created.
Changes from v1
(https://lore.kernel.org/linux-block/[email protected]/)
- use 'bool' parameter type (Jürgen Groß)
- Let blkfront can also disable the feature from its side
(Roger Pau Monné)
- Avoid unnecessary xenbus_printf (Roger Pau Monné)
- Update frontend parameter doc
SeongJae Park (3):
xen-blkback: add a parameter for disabling of persistent grants
xen-blkfront: add a parameter for disabling of persistent grants
xen-blkfront: Apply changed parameter name to the document
.../ABI/testing/sysfs-driver-xen-blkback | 9 ++++++++
.../ABI/testing/sysfs-driver-xen-blkfront | 11 +++++++++-
drivers/block/xen-blkback/xenbus.c | 22 ++++++++++++++-----
drivers/block/xen-blkfront.c | 20 ++++++++++++-----
4 files changed, 50 insertions(+), 12 deletions(-)
--
2.17.1
From: SeongJae Park <[email protected]>
Commit 14e710fe7897 ("xen-blkfront: rename indirect descriptor
parameter") changed the name of the module parameter for the maximum
amount of segments in indirect requests but missed updating the
document. This commit updates the document.
Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Acked-by: Roger Pau Monné <[email protected]>
---
Documentation/ABI/testing/sysfs-driver-xen-blkfront | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
index 9c31334cb2e6..28008905615f 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkfront
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront
@@ -1,4 +1,4 @@
-What: /sys/module/xen_blkfront/parameters/max
+What: /sys/module/xen_blkfront/parameters/max_indirect_segments
Date: June 2013
KernelVersion: 3.11
Contact: Konrad Rzeszutek Wilk <[email protected]>
--
2.17.1
From: SeongJae Park <[email protected]>
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 <[email protected]>
Signed-off-by: SeongJae Park <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Acked-by: Roger Pau Monné <[email protected]>
---
.../ABI/testing/sysfs-driver-xen-blkback | 9 ++++++++
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 <[email protected]>
+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 b9aa5d1ac10b..8fc34211dc8b 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -474,6 +474,12 @@ 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)
@@ -519,6 +525,8 @@ 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;
@@ -906,7 +914,8 @@ static void connect(struct backend_info *be)
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);
@@ -1067,7 +1076,6 @@ 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;
@@ -1093,9 +1101,11 @@ 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;
/*
@@ -1118,7 +1128,7 @@ 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);
--
2.17.1