On 8/28/24 7:49 AM, Manish Pandey wrote:
'Commit af550e4c9682 ("block/blk-mq: Don't complete locally if
capacities are different")' enforces to complete the request locally
only if the submission and completion CPUs have same capacity.
To have optimal IO load balancing or to avoid contention b/w submission
path and completion path, user may need to complete IO request of large
capacity CPU(s) on Small Capacity CPU(s) or vice versa.
Hence introduce a QUEUE_FLAG_ALLOW_DIFF_CAPACITY blk queue flag to let
user decide if it wants to complete the request locally or need an IPI
even if the capacity of the requesting and completion queue is different.
This gives flexibility to user to choose best CPU for their completion
to give best performance for their system.
I think that the following is missing from the above description:
- Mentioning that this is for an unusual interrupt routing technology
(SoC sends the interrupt to another CPU core than what has been
specified in the smp_affinity mask).
- An explanation why the desired effect cannot be achieved by changing
rq_affinity into 0.
block/blk-mq-debugfs.c | 1 +
block/blk-mq.c | 3 ++-
block/blk-sysfs.c | 12 ++++++++++--
include/linux/blkdev.h | 1 +
4 files changed, 14 insertions(+), 3 deletions(-)
Since the semantics of a sysfs attribute are modified,
Documentation/ABI/stable/sysfs-block should be updated.
Thanks,
Bart.
