Re: CFQ idling kills I/O performance on ext4 with blkio cgroup controller

From: Paolo Valente
Date: Thu Jun 13 2019 - 12:50:45 EST

> Il giorno 12 giu 2019, alle ore 00:34, Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx> ha scritto:
> On 6/2/19 12:04 AM, Srivatsa S. Bhat wrote:
>> On 5/30/19 3:45 AM, Paolo Valente wrote:
> [...]
>>> At any rate, since you pointed out that you are interested in
>>> out-of-the-box performance, let me complete the context: in case
>>> low_latency is left set, one gets, in return for this 12% loss,
>>> a) at least 1000% higher responsiveness, e.g., 1000% lower start-up
>>> times of applications under load [1];
>>> b) 500-1000% higher throughput in multi-client server workloads, as I
>>> already pointed out [2].
>> I'm very happy that you could solve the problem without having to
>> compromise on any of the performance characteristics/features of BFQ!
>>> I'm going to prepare complete patches. In addition, if ok for you,
>>> I'll report these results on the bug you created. Then I guess we can
>>> close it.
>> Sounds great!
> Hi Paolo,


> Hope you are doing great!

Sort of, thanks :)

> I was wondering if you got a chance to post these patches to LKML for
> review and inclusion... (No hurry, of course!)

I'm having troubles testing these new patches on 5.2-rc4. As it
happened with the first release candidates for 5.1, the CPU of my test
machine (Intel Core i7-2760QM@xxxxxxx) is so slowed down that results
are heavily distorted with every I/O scheduler.

Unfortunately, I'm not competent enough to spot the cause of this
regression in a feasible amount of time. I hope it'll go away with
next release candidates, or I'll test on 5.1.

> Also, since your fixes address the performance issues in BFQ, do you
> have any thoughts on whether they can be adapted to CFQ as well, to
> benefit the older stable kernels that still support CFQ?

I have implanted my fixes on the existing throughput-boosting
infrastructure of BFQ. CFQ doesn't have such an infrastructure.

If you need I/O control with older kernels, you may want to check my
version of BFQ for legacy block, named bfq-sq and available in this

I'm willing to provide you with any information or help if needed.


> Thank you!
> Regards,
> Srivatsa
> VMware Photon OS

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