Messages in this thread | | | From | Michael Stapelberg <> | Date | Mon, 21 Jun 2021 11:20:10 +0200 | Subject | Re: [PATCH] backing_dev_info: introduce min_bw/max_bw limits |
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Hey Miklos
On Fri, 18 Jun 2021 at 16:42, Miklos Szeredi <miklos@szeredi.hu> wrote: > > On Fri, 18 Jun 2021 at 10:31, Michael Stapelberg > <stapelberg+linux@google.com> wrote: > > > Maybe, but I don’t have the expertise, motivation or time to > > investigate this any further, let alone commit to get it done. > > During our previous discussion I got the impression that nobody else > > had any cycles for this either: > > https://lore.kernel.org/linux-fsdevel/CANnVG6n=ySfe1gOr=0ituQidp56idGARDKHzP0hv=ERedeMrMA@mail.gmail.com/ > > > > Have you had a look at the China LSF report at > > http://bardofschool.blogspot.com/2011/? > > The author of the heuristic has spent significant effort and time > > coming up with what we currently have in the kernel: > > > > """ > > Fengguang said he draw more than 10K performance graphs and read even > > more in the past year. > > """ > > > > This implies that making changes to the heuristic will not be a quick fix. > > Having a piece of kernel code sitting there that nobody is willing to > fix is certainly not a great situation to be in.
Agreed.
> > And introducing band aids is not going improve the above situation, > more likely it will prolong it even further.
Sounds like “Perfect is the enemy of good” to me: you’re looking for a perfect hypothetical solution, whereas we have a known-working low risk fix for a real problem.
Could we find a solution where medium-/long-term, the code in question is improved, perhaps via a Summer Of Code project or similar community efforts, but until then, we apply the patch at hand?
As I mentioned, I think adding min/max limits can be useful regardless of how the heuristic itself changes.
If that turns out to be incorrect or undesired, we can still turn the knobs into a no-op, if removal isn’t an option.
Thanks Best regards Michael
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