switch block layer polling to a bio based model v4

[Jens Axboe]

On 10/12/21 8:57 AM, Sagi Grimberg wrote:
> 
>>> Hi all,
>>>
>>> This series clean up the block polling code a bit and changes the interface
>>> to poll for a specific bio instead of a request_queue and cookie pair.
>>>
>>> Polling for the bio itself leads to a few advantages:
>>>
>>>    - the cookie construction can made entirely private in blk-mq.c
>>>    - the caller does not need to remember the request_queue and cookie
>>>      separately and thus sidesteps their lifetime issues
>>>    - keeping the device and the cookie inside the bio allows to trivially
>>>      support polling BIOs remapping by stacking drivers
>>>    - a lot of code to propagate the cookie back up the submission path can
>>>      removed entirely
>>>
>>> The one major caveat is that this requires RCU freeing polled BIOs to make
>>> sure the bio that contains the polling information is still alive when
>>> io_uring tries to poll it through the iocb. For synchronous polling all the
>>> callers have a bio reference anyway, so this is not an issue.
>>
>> I ran this through the usual peak testing, and it doesn't seem to regress
>> anything for me. We're still at around ~7.4M polled IOPS on a single CPU
>> core:
>>
>> taskset -c 0,16 t/io_uring -d128 -b512 -s32 -c32 -p1 -F1 -B1 -D1 -n2 /dev/nvme1n1 /dev/nvme2n1
>> Added file /dev/nvme1n1 (submitter 0)
>> Added file /dev/nvme2n1 (submitter 1)
>> polled=1, fixedbufs=1, register_files=1, buffered=0, QD=128
>> Engine=io_uring, sq_ring=128, cq_ring=256
>> submitter=0, tid=1199
>> submitter=1, tid=1200
>> IOPS=7322112, BW=3575MiB/s, IOS/call=32/31, inflight=(110 71)
>> IOPS=7452736, BW=3639MiB/s, IOS/call=32/31, inflight=(52 80)
>> IOPS=7419904, BW=3623MiB/s, IOS/call=32/31, inflight=(78 104)
>> IOPS=7392576, BW=3609MiB/s, IOS/call=32/32, inflight=(75 102)
> 
> Jens, is that with nvme_core.multipath=Y ?

No, I don't have multipath enabled. I can run that too, if you'd like.

-- 
Jens Axboe