Re: [PATCH V3 00/11] block-throttle: add .high limit

From	Tejun Heo <tj@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH V3 00/11] block-throttle: add .high limit
Date	2016-10-04 22:30 +0200
Message-ID	<soEvD-7yl-11@gated-at.bofh.it> (permalink)
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Hello, Paolo.

On Tue, Oct 04, 2016 at 09:29:48PM +0200, Paolo Valente wrote:
> > Hmm... I think we already discussed this but here's a really simple
> > case.  There are three unknown workloads A, B and C and we want to
> > give A certain best-effort guarantees (let's say around 80% of the
> > underlying device) whether A is sharing the device with B or C.
> 
> That's the same example that you proposed me in our previous
> discussion.  For this example I showed you, with many boring numbers,
> that with BFQ you get the most accurate distribution of the resource.

Yes, it is about the same example and what I understood was that
"accurate distribution of the resources" holds as long as the
randomness is incidental (ie. due to layout on the filesystem and so
on) with the slice expiration mechanism offsetting the actually random
workloads.

> If you have enough stamina, I can repeat them again.  To save your

I'll go back to the thread and re-read them.

> patience, here is a very brief summary.  In a concrete use case, the
> unknown workloads turn into something like this: there will be a first
> time interval during which A happens to be, say, sequential, B happens
> to be, say, random and C happens to be, say, quasi-sequential.  Then
> there will be a next time interval during which their characteristics
> change, and so on.  It is easy (but boring, I acknowledge it) to show
> that, for each of these time intervals BFQ provides the best possible
> service in terms of fairness, bandwidth distribution, stability and so
> on.  Why?  Because of the elastic bandwidth-time scheduling of BFQ
> that we already discussed, and because BFQ is naturally accurate in
> redistributing aggregate throughput proportionally, when needed.

Yeah, that's what I remember and for workload above certain level of
randomness its time consumption is mapped to bw, right?

> > I get that bfq can be a good compromise on most desktop workloads and
> > behave reasonably well for some server workloads with the slice
> > expiration mechanism but it really isn't an IO resource partitioning
> > mechanism.
> 
> Right.  My argument is that BFQ enables you to give to each client the
> bandwidth and low-latency guarantees you want.  And this IMO is way
> better than partitioning a resource and then getting unavoidable
> unfairness and high latency.

But that statement only holds while bw is the main thing to guarantee,
no?  The level of isolation that we're looking for here is fairly
strict adherence to sub/few-milliseconds in terms of high percentile
scheduling latency while within the configured bw/iops limits, not
"overall this device is being used pretty well".

Thanks.

-- 
tejun

Thread

[PATCH V3 00/11] block-throttle: add .high limit Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 10/11] block-throttle: add a simple idle detection Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 07/11] blk-throttle: make throtl_slice tunable Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 08/11] blk-throttle: detect completed idle cgroup Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 06/11] blk-throttle: make sure expire time isn't too big Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 11/11] blk-throttle: ignore idle cgroup limit Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 09/11] block-throttle: make bandwidth change smooth Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 03/11] block-throttle: configure bps/iops limit for cgroup in high limit Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 01/11] block-throttle: prepare support multiple limits Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  [PATCH v3 02/11] block-throttle: add .high interface Shaohua Li <shli@fb.com> - 2016-10-03 23:30 +0200
  Re: [PATCH V3 00/11] block-throttle: add .high limit Vivek Goyal <vgoyal@redhat.com> - 2016-10-04 15:30 +0200
    Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 18:00 +0200
      Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 18:30 +0200
        Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 19:10 +0200
          Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 19:50 +0200
            Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 21:00 +0200
              Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 21:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 21:20 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 21:40 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 22:30 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-05 14:40 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Vivek Goyal <vgoyal@redhat.com> - 2016-10-05 15:20 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-05 16:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-05 17:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-05 21:50 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-05 22:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 10:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 15:20 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Vivek Goyal <vgoyal@redhat.com> - 2016-10-06 19:50 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 20:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Vivek Goyal <vgoyal@redhat.com> - 2016-10-06 20:40 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 23:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Mark Brown <broonie@kernel.org> - 2016-10-06 21:50 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-07 00:30 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-05 22:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 09:30 +0200
                Fwd: [PATCH V3 00/11] block-throttle: add .high limit Kyle Sanderson <kyle.leet@gmail.com> - 2016-10-09 03:20 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Linus Walleij <linus.walleij@linaro.org> - 2016-10-06 10:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Mark Brown <broonie@kernel.org> - 2016-10-06 13:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-10-06 14:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 15:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-10-06 16:00 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-06 17:10 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-10-06 17:20 +0200
                Re: [PATCH V3 00/11] block-throttle: add .high limit Heinz Diehl <htd+ml@fritha.org> - 2016-10-08 12:50 +0200
            Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 21:50 +0200
      Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 18:30 +0200
      Re: [PATCH V3 00/11] block-throttle: add .high limit Vivek Goyal <vgoyal@redhat.com> - 2016-10-04 20:20 +0200
        Re: [PATCH V3 00/11] block-throttle: add .high limit Tejun Heo <tj@kernel.org> - 2016-10-04 21:00 +0200
          Re: [PATCH V3 00/11] block-throttle: add .high limit Paolo Valente <paolo.valente@unimore.it> - 2016-10-04 21:00 +0200

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