| Message ID | 20200922105209.5284-3-sjpark@amazon.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xen-blk(back|front): Let users disable persistent grants | expand |
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
On Tue, 22 Sep 2020 14:11:32 +0200 "Jürgen Groß" <jgross@suse.com> wrote: > 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/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
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);