[PATCH 0/2] lio-target: Add per iSCSI connection CPU scheduling affinity

[Nicholas A. Bellinger]

From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

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!

Signed-off-by: Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx>

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(-)
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