This patch builds ATA commands with high priority if the iocontext of a process is set to real time. The goal of the patch is to improve tail latencies of workloads that use higher queue depths. This patch has been tested with an Ultrastar HE8 HDD and cuts the the p99.99 tail latency of foreground IO from 2s down to 72ms when using the deadline scheduler. This patch works independently of the scheduler so it can be used with all of the currently available request based schedulers. Foreground IO, for the previously described results, is an async fio job submitting 4K read requests at a QD of 1 to the HDD. The foreground IO is set with the iopriority class of real time. The background workload is another fio job submitting read requests at a QD of 32 to the same HDD with default iopriority. This feature is enabled by setting a queue flag that is exposed as a sysfs entry named req_prio. If this feature is enabled the request ioprio comes from the highest priority between the iocontext and the bio. v2: - Add queue flag to set iopriority going to the request - If queue flag set, send iopriority class to ata_build_rw_tf - Remove redundant code in ata_ncq_prio_enabled function. Adam Manzanares (2): ata: Enabling ATA Command Priorities block: Add iocontext priority to request block/blk-core.c | 8 +++++++- block/blk-sysfs.c | 32 ++++++++++++++++++++++++++++++++ include/linux/blkdev.h | 2 ++ 3 files changed, 41 insertions(+), 1 deletion(-) -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
