On Tue, 22 Sep 2020 16:25:57 +0200 "Jürgen Groß" <jgross@xxxxxxxx> wrote: > On 22.09.20 16:15, SeongJae Park wrote: > > 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 | 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@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..f4c8827fa0ad 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 ? 1 : 0; > > Just assign the value instead of using the ternary operator? I will do so in the next version. > > With that changed you can add my > > Reviewed-by: Juergen Gross <jgross@xxxxxxxx> Thank you for your kind, quick, and detailed review! Thanks, SeongJae Park
