As I see, since megaraid will have 1:1 mapping of CPU to hw queue, will
there only ever possibly a single bit set in ctx_map? If so, it seems a
waste to always check every sbitmap map. But adding logic for this may
negate any possible gains.
It really depends on min and max cpu id in the map, then sbitmap
depth can be reduced to (max - min + 1). I'd suggest to double check that
cost of sbitmap_any_bit_set() really matters.
Hi Ming,
I'm not sure that reducing the search range would help much, as we still
need to load some indexes of map[], and at best this may be reduced from
2/3 -> 1 elements, depending on nr_cpus.
for
none because request may not be dispatched successfully by direct
issue.
When block layer attempt posting request to h/w queue directly (for
ioscheduler=none) and if it fails, it is calling
blk_mq_request_bypass_insert().
blk_mq_request_bypass_insert function will start the h/w queue from
submission context. Do we still have an issue if we skip running hw
queue from completion ?
The thing is that we can't guarantee that direct issue or adding request
into
hctx->dispatch is always done for MQ/none, for example, request still
can be added to sw queue from blk_mq_flush_plug_list() when mq plug is
applied.
I see even blk_mq_sched_insert_requests() from blk_mq_flush_plug_list make
sure it run the h/w queue. If all the submission path which deals with s/w
queue make sure they run h/w queue, can't we remove blk_mq_run_hw_queues()
from scsi_end_request ?
No, one purpose of blk_mq_run_hw_queues() is for rerun queue in case that
dispatch budget is running out of in submission path, and sdev->device_busy is
shared by all hw queues on this scsi device.
I posted one patch for avoiding it in scsi_end_request() before, looks it
never lands upstream:
I saw that you actually posted the v3:
https://lore.kernel.org/linux-scsi/BL0PR2101MB11230C5F70151037B23C0C35CE2D0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
And it no longer applies, due to the changes in scsi_mq_get_budget(), I
think, which look non-trivial. Any chance to repost?
OK, will post V4.
Thanks!
