On Tue, 22 Sep 2020 14:11:32 +0200 "Jürgen Groß" <jgross@xxxxxxxx> wrote: > On 22.09.20 12:52, 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. It can be disabled from blkback side using a > > module parameter, 'feature_persistent'. But, it is impossible from > > blkfront side. For the reason, this commit adds a blkfront module > > parameter for disabling of the feature. > > > > [1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability > > > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > > --- > > .../ABI/testing/sysfs-driver-xen-blkfront | 9 ++++++ > > drivers/block/xen-blkfront.c | 28 +++++++++++++------ > > 2 files changed, 29 insertions(+), 8 deletions(-) > > [...] > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > > index 91de2e0755ae..49c324f377de 100644 > > --- a/drivers/block/xen-blkfront.c > > +++ b/drivers/block/xen-blkfront.c > > @@ -149,6 +149,13 @@ static unsigned int xen_blkif_max_ring_order; > > module_param_named(max_ring_page_order, xen_blkif_max_ring_order, int, 0444); > > MODULE_PARM_DESC(max_ring_page_order, "Maximum order of pages to be used for the shared ring"); > > > > +/* 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"); > > + > > + > > #define BLK_RING_SIZE(info) \ > > __CONST_RING_SIZE(blkif, XEN_PAGE_SIZE * (info)->nr_ring_pages) > > > > @@ -1866,11 +1873,13 @@ static int talk_to_blkback(struct xenbus_device *dev, > > message = "writing protocol"; > > goto abort_transaction; > > } > > - err = xenbus_printf(xbt, dev->nodename, > > - "feature-persistent", "%u", 1); > > - if (err) > > - dev_warn(&dev->dev, > > - "writing persistent grants feature to xenbus"); > > + if (feature_persistent) { > > + err = xenbus_printf(xbt, dev->nodename, > > + "feature-persistent", "%u", 1); > > + if (err) > > + dev_warn(&dev->dev, > > + "writing persistent grants feature to xenbus"); > > + } > > > > err = xenbus_transaction_end(xbt, 0); > > if (err) { > > @@ -2316,9 +2325,12 @@ static void blkfront_gather_backend_features(struct blkfront_info *info) > > if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0)) > > blkfront_setup_discard(info); > > > > - info->feature_persistent = > > - !!xenbus_read_unsigned(info->xbdev->otherend, > > - "feature-persistent", 0); > > + if (feature_persistent) > > + info->feature_persistent = > > + !!xenbus_read_unsigned(info->xbdev->otherend, > > + "feature-persistent", 0); > > + else > > + info->feature_persistent = 0; > > > > indirect_segments = xenbus_read_unsigned(info->xbdev->otherend, > > "feature-max-indirect-segments", 0); > > > > Here you have the same problem as in blkback: feature_persistent could > change its value between the two tests. Yes, indeed. I will fix this in the next version. Thanks, SeongJae Park
