Re: [PATCH] block/mq-deadline: Speed up the dispatch of low-priority requests

[Jens Axboe <axboe@kernel.dk>]

On 8/26/21 6:03 PM, Bart Van Assche wrote:
> On 8/26/21 4:51 PM, Jens Axboe wrote:
>> On 8/26/21 5:49 PM, Bart Van Assche wrote:
>>> On 8/26/21 11:45 AM, Jens Axboe wrote:
>>>> Just ran a quick test here, and I go from 3.55M IOPS to 1.23M switching
>>>> to deadline, of which 37% of the overhead is from dd_dispatch().
>>>>
>>>> With the posted patch applied, it runs at 2.3M IOPS with mq-deadline,
>>>> which is a lot better. This is on my 3970X test box, so 32 cores, 64
>>>> threads.
>>>
>>> Hi Jens,
>>>
>>> With the script below, queue depth >= 2 and an improved version of
>>> Zhen's patch I see 970 K IOPS with the mq-deadline scheduler in an
>>> 8 core VM (i7-4790 CPU). In other words, more IOPS than what Zhen
>>> reported with fewer CPU cores. Is that good enough?
>>
>> That depends, what kind of IOPS are you getting if you revert the
>> original change?
> 
> Hi Jens,
> 
> Here is an overview of the tests I ran so far, all on the same test
> setup:
> * No I/O scheduler:               about 5630 K IOPS.
> * Kernel v5.11 + mq-deadline:     about 1100 K IOPS.
> * block-for-next + mq-deadline:   about  760 K IOPS.
> * block-for-next with improved mq-deadline performance: about 970 K IOPS.

So we're still off by about 12%, I don't think that is good enough.
That's assuming that v5.11 + mq-deadline is the same as for-next with
the mq-deadline change reverted? Because that would be the key number to
compare it with.

-- 
Jens Axboe