Re: [RFC 0/4] completion locking optimisation feature

[Jens Axboe <axboe@kernel.dk>]

On 3/18/22 9:00 AM, Pavel Begunkov wrote:
> On 3/18/22 14:52, Jens Axboe wrote:
>> On 3/18/22 8:42 AM, Pavel Begunkov wrote:
>>> On 3/18/22 13:52, Pavel Begunkov wrote:
>>>> A WIP feature optimising out CQEs posting spinlocking for some use cases.
>>>> For a more detailed description see 4/4.
>>>>
>>>> Quick benchmarking with fio/t/io_uring nops gives extra 4% to throughput for
>>>> QD=1, and ~+2.5% for QD=4.
>>>
>>> Non-io_uring overhead (syscalls + userspace) takes ~60% of all execution
>>> time, so the percentage should quite depend on the CPU and the kernel config.
>>> Likely to be more than 4% for a faster setup.
>>>
>>> fwiw, was also usingIORING_ENTER_REGISTERED_RING, if it's not yet included
>>> in the upstream version of the tool.
>>
>> But that seems to be exclusive of using PRIVATE_CQ?
> 
> No, it's not. Let me ask to clarify the description and so, why do you
> think it is exclusive?

Didn't dig too deep, just saw various EINVAL around registered files and
updating/insertion. And the fact that t/io_uring gets -EINVAL on
register with op 20 (ring fd) if I set CQ_PRIVATE, see other email.

-- 
Jens Axboe