User`s guide

Appendix A Other Changes

The following sections describe other features of Unbreakable Enterprise Kernel Release 3 (UEK R3). The

mainline version in which a feature was introduced is noted in parentheses.

A.1 Architecture

• vsysscall emulation and vsyscall parameter. (3.1)

• INTEL_MID configuration. (3.1)

• mrst_pmu driver for Intel Moorestown Power Management Unit. (3.1)

• Hardware memory error recovery support for ACPI, APEI, and GHES. (3.1)

• printk() support for recoverable error via NMI for ACPI, APEI, and GHES. (3.1)

A.2 Block Devices

• Strict CPU affinity can be enabled by setting the value of /sys/block/blkdev/queue/rq_affinity

to 2. Performance on some systems benefits from being directed to the strict requester CPU rather than

using per-socket steering. (3.1)

• CFQ I/O scheduler performance tuning adds think time check for a group, which makes bandwidth

usage more efficient by not leaving queues active when there are no further requests for the group. (3.1)

• Flakey target support in the device mapper adds the corrupt_bio_byte parameter to simulate

corruption by overwriting a byte at a specified position with a specified value while the device is down.

The drop_writes option parameter drops writes silently while the device is down. (3.1)

• The device mapper supports MD RAID-1 personality through the dm-raid target. (3.1)

• The device mapper supports the ability to parse and use metadata devices with dm-raid. Without the

metadata devices, many RAID features would be unavailable. (3.1)

• Experimental support for thin provisioning in the device mapper allows the creation of multiple thinly

provisioned volumes from a storage pool and recursive snapshots to an arbitrary depth. (3.2)

• I/O-less dirty throttling and reduced file-system writeback from page reclamation greatly reduces I/O

seeks and CPU contention. (3.2)

• The cfq_target_latency parameter under sysfs allows throughput and read latency to be tuned.

(3.4)

• The device mapper supports adding and removing space at the end of the devices when resizing

RAID-10 arrays with near and offset layouts. (3.4)

• Thin target in the device mapper supports discards. When non-discard I/O completes and the

associated mappings are quiesced, any discards that were deferred (via ds_add_work() in

process_discard()) are queued for processing by the worker thread. (3.4)

• Thin target in the device mapper provides user-space access to pool metadata. Two new messages can

be sent to the thin pool target allowing it to take a snapshot of the metadata. This read-only snapshot

can be accessed from user space concurrently with the live target. (3.5)

• Thin target in the device mapper uses dedicated slab caches (whose names are prefixed with dm_)

rather than relying on kmalloc memory pools backed by generic slab caches. This allows independent

accounting of memory usage and any associated memory leakage by thin provisioning. (3.5)