From: SeongJae Park <sjpark@xxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> --- .../ABI/testing/sysfs-driver-xen-blkback | 9 ++++++ drivers/block/xen-blkback/xenbus.c | 28 ++++++++++++++----- 2 files changed, 30 insertions(+), 7 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@xxxxxxxxx> +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..8a95ddd08b13 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -879,6 +879,12 @@ static void reclaim_memory(struct xenbus_device *dev) /* ** Connection ** */ +/* 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"); + /* * Write the physical details regarding the block device to the store, and * switch to Connected state. @@ -906,11 +912,15 @@ 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); - if (err) { - xenbus_dev_fatal(dev, err, "writing %s/feature-persistent", - dev->nodename); - goto abort; + if (feature_persistent) { + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", + "%u", feature_persistent); + if (err) { + xenbus_dev_fatal(dev, err, + "writing %s/feature-persistent", + dev->nodename); + goto abort; + } } err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu", @@ -1093,8 +1103,12 @@ 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); + if (feature_persistent) + pers_grants = xenbus_read_unsigned(dev->otherend, + "feature-persistent", 0); + else + pers_grants = 0; + blkif->vbd.feature_gnt_persistent = pers_grants; blkif->vbd.overflow_max_grants = 0; -- 2.17.1
