Re: [PATCH v7] block: Improve IOPS by removing the fairness code

[Jens Axboe <axboe@kernel.dk>]

On 5/30/24 3:17 PM, Keith Busch wrote:
> On Thu, May 30, 2024 at 02:02:20PM -0700, Bart Van Assche wrote:
>> Thank you for having run this test. I propose that users who want better
>> fairness than what my patch supports use an appropriate mechanism for
>> improving fairness (e.g. blk-iocost or blk-iolat). This leaves the choice
>> between maximum performance and maximum fairness to the user. Does this
>> sound good to you?
> 
> I really don't know, I generally test with low latency devices and
> disable those blk services because their overhead is too high. I'm
> probably not the target demographic for those mechanisms. :)

Yeah same. But outside of that, needing to configure something else is
also a bit of a cop out. From the initial posting, it's quoting 2.9%
gain. For lots of cases, adding blk-iocost or blk-iolat would be MORE
than a 2.9% hit.

That said, I'd love to kill the code, but I still don't think we have
good numbers on it. Are yours fully stable? What does the qd=1 test do
_without_ having anyone compete with it? Is the bandwidth nicely
balanced if each does qd=32? I'm again kindly asking for some testing
:-)

> I just wanted to push the edge cases to see where things diverge.
> Perhaps Jens can weigh in on the impact and suggested remedies?

Don't think we have enough data yet to make the call...

-- 
Jens Axboe