Messages in this thread | | | Subject | Re: [PATCH v2 2/3] xen-blkfront: add a parameter for disabling of persistent grants | From | Jürgen Groß <> | Date | Tue, 22 Sep 2020 14:11:32 +0200 |
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On 22.09.20 12:52, SeongJae Park wrote: > From: SeongJae Park <sjpark@amazon.de> > > 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@amazon.de> > --- > .../ABI/testing/sysfs-driver-xen-blkfront | 9 ++++++ > drivers/block/xen-blkfront.c | 28 +++++++++++++------ > 2 files changed, 29 insertions(+), 8 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkfront b/Documentation/ABI/testing/sysfs-driver-xen-blkfront > index c0a6cb7eb314..9c31334cb2e6 100644 > --- a/Documentation/ABI/testing/sysfs-driver-xen-blkfront > +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkfront > @@ -8,3 +8,12 @@ Description: > is 32 - higher value means more potential throughput but more > memory usage. The backend picks the minimum of the frontend > and its default backend value. > + > +What: /sys/module/xen_blkfront/parameters/feature_persistent > +Date: September 2020 > +KernelVersion: 5.10 > +Contact: SeongJae Park <sjpark@amazon.de> > +Description: > + Whether to enable the persistent grants feature or not. Note > + that this option only takes effect on newly created frontends. > + The default is Y (enable). > 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.
Juergen
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