lio-target: Add per iSCSI connection CPU scheduling affinity

From: Nicholas Bellinger <[email protected]>

Grettings all,

This patch series adds support for the automatic setting of CPU scheduling affinity for iscsi_ttx and iscsi_trx kernel thread set pairs on a per iSCSI connection context basis using a newly defined struct iscsi_conn->conn_cpumask.

This code was originally inspiried by a discussion last year at LinuxCon with Philipp Reisner about how CPU affinity is determined for asender, worker, receiver for each DRBD resource + underlying struct block_device. This patch series for LIO-Target follows a similar model for ensuring that each iSCSI connection's RX / TX pair as scheduled to execute on the same CPU to take advantage of hot caching effects for shared per iSCSI connection data structures.

The first patch adds support for a iscsi_global->ts_bitmap to handle the proper atomic allocation of each thread_id using bitmap_find_free_region() and it's release with bitmap_release_region(). The important item here is that the lowest available thread_id in iscsi_allocate_thread_sets() with iscsi_global->ts_bitmap will always be used.

The second patch adds the primary iscsi_thread_get_cpumask() and iscsi_thread_check_cpumask() callers, and updates the iSCSI login / connection setup patch and the main RX / TX processing loops to check for a updated call set_cpus_allowed_ptr(). This patch also updates the per iSCSI connection release and exeception paths to call free_cpumask_var() for struct iscsi_conn->conn_cpumask.

Many thanks again to Philip Reiser and the DRBD/Linbit team for insight into this optimization for LIO-Target!

Nicholas Bellinger (2):
lio-target: Convert to use bitmap for handling thread_id allocation
lio-target: Add support for per iSCSI connection CPU scheduling
affinity

 drivers/target/lio-target/iscsi_target.c       |   96 +++++++++++++++++++++++-
 drivers/target/lio-target/iscsi_target.h       |    1 +
 drivers/target/lio-target/iscsi_target_core.h  |   12 +++-
 drivers/target/lio-target/iscsi_target_login.c |   23 ++++++
 drivers/target/lio-target/iscsi_thread_queue.c |   58 +++++++++++++-
 drivers/target/lio-target/iscsi_thread_queue.h |    5 +
 6 files changed, 184 insertions(+), 11 deletions(-)