Il giorno 4 ott 2019, alle ore 20:17, Dusty Mabe dusty@dustymabe.com ha scritto:
On 10/4/19 1:48 PM, Paolo Valente wrote:
Il giorno 4 ott 2019, alle ore 19:21, Dusty Mabe dusty@dustymabe.com ha scritto:
Just checking this one point: On Fedora and Fedora CoreOS (assuming we don't change any defaults) users won't need to do anything to "enable this boost". Correct?
Thank you very much for this useful question; it helped me realize that I didn't explain the main problem at all, sorry.
The answer to your question is yes and no. The 'yes' is because, BFQ is already there, as you rightly point out.
The 'no' is the tricky part. The main issue is that BFQ cannot make a disk reach a higher throughput than that requested by the workload. Let me give a simple example. If the only process doing I/O on a disk does a read of 1 MB every second, then the maximum possible throughput that can be reached by the disk is 1 MB/s. A bad solution for controlling I/O may cause throughput to be below 1 MB/s, but no solution could go above 1 MB/s, simply because no more than that is being requested.
So, if a user/sysadmin keeps disk bandwidths underutilized, because this is their long-standing practice for guaranteeing bandwidth and latency, and because they are not aware of what they can now do with BFQ, then nothing changes for them, even if now I/O is scheduled by BFQ.
I hope my concern is clearer now.
My interpretation of what you're saying is:
"BFQ is there now, but people will need to change their applications/workloads to really take advantage of it.
Yes. More precisely, this holds true for professionals (or power users), who configure/size their storage resources so as to keep the latter underutilized.
Now that this message seems clear, let me complete the picture. There is one more (and last) set of professionals who would see no benefit: those who use throttling-based solutions to control I/O. BFQ cannot boost throughput for them, because throughput is forcibly choked by throttling. The solution is just to stop using throttling.
I think this is more or less all.
Thank you again for your questions, Paolo
Is that correct?
The goal of this topic is to spread the word, and offer help.
Thanks to you!