On Tue, Sep 22, 2020 at 09:01:25AM +0200, SeongJae Park wrote: > From: SeongJae Park <sjpark@xxxxxxxxx> > > Persistent grants feature provides high scalability. On some small > systems, however, it could incur data copy overhead[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. Would it be better suited to have it per guest? > > [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 | 8 ++++++++ > drivers/block/xen-blkback/xenbus.c | 17 ++++++++++++++--- > 2 files changed, 22 insertions(+), 3 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback > index ecb7942ff146..0c42285c75ee 100644 > --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback > +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback > @@ -35,3 +35,11 @@ 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. > + The default is 1 (enable). > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > index b9aa5d1ac10b..9c03d70469f4 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 unsigned int feature_persistent = 1; > +module_param_named(feature_persistent, feature_persistent, int, 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. > @@ -906,7 +912,8 @@ 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", > + feature_persistent ? 1 : 0); > if (err) { > xenbus_dev_fatal(dev, err, "writing %s/feature-persistent", > dev->nodename); > @@ -1093,8 +1100,12 @@ 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 >
