Hi James, This series is about reducing locking contention in the IO submission/response processing fast path of libiscsi and the various iscsi transports usage of libiscsi code.
We replace the session lock with two locks, a forward lock and a backwards lock named frwd_lock and back_lock respectively. The forward lock protects resources that change while sending a request to the target, such as cmdsn, queued_cmdsn, and allocating task from the commands' pool with kfifo_out. The backward lock protects resources that change while processing a response or in error path, such as cmdsn_exp, cmdsn_max, and returning tasks to the commands' pool with kfifo_in. The 1st patch in the series is a restructuring patch for iscsi_tcp r2t response logic, the 2nd is the main patch and the 3rd is cleanup asked by Mike who reviewed the whole series when we posted in over the open-iscsi mailing list. Under a "steady state" fast-path situation, that is when one or more processes/threads submit IO to an iscsi device and a single kernel upcall (e.g softirq) is dealing with processing of responses without errors, this patch eliminates the contention between the queuecommand()/request response/scsi_done() associated with iscsi sessions. Or and Shlomo. Shlomo Pongratz (3): SCSI/libiscsi: Restructure iscsi_tcp r2t response logic SCSI/libiscsi: Reduce locking contention in fast path SCSI/libiscsi: Remove unneeded code drivers/scsi/be2iscsi/be_main.c | 26 ++-- drivers/scsi/bnx2i/bnx2i_hwi.c | 46 ++++---- drivers/scsi/bnx2i/bnx2i_iscsi.c | 8 +- drivers/scsi/iscsi_tcp.c | 22 ++-- drivers/scsi/libiscsi.c | 226 ++++++++++++++++++++------------------ drivers/scsi/libiscsi_tcp.c | 71 +++++++----- drivers/scsi/qla4xxx/ql4_isr.c | 4 +- include/scsi/libiscsi.h | 17 ++- include/scsi/libiscsi_tcp.h | 2 + 9 files changed, 228 insertions(+), 194 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
