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

From	Paolo Valente <paolo.valente@unimore.it>
Newsgroups	linux.kernel
Subject	Re: [PATCH V3 00/11] block-throttle: add .high limit
Date	2016-10-04 19:10 +0200
Message-ID	<soBo6-5Ek-9@gated-at.bofh.it> (permalink)
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> Il giorno 04 ott 2016, alle ore 18:27, Tejun Heo <tj@kernel.org> ha scritto:
> 
> Hello,
> 
> On Tue, Oct 04, 2016 at 06:22:28PM +0200, Paolo Valente wrote:
>> Could you please elaborate more on this point?  BFQ uses sectors
>> served to measure service, and, on the all the fast devices on which
>> we have tested it, it accurately distributes
>> bandwidth as desired, redistributes excess bandwidth with any issue,
>> and guarantees high responsiveness and low latency at application and
>> system level (e.g., ~0 drop rate in video playback, with any background
>> workload tested).
> 
> The same argument as before.  Bandwidth is a very bad measure of IO
> resources spent.  For specific use cases (like desktop or whatever),
> this can work but not generally.
> 

Actually, we have already discussed this point, and IMHO the arguments
that (apparently) convinced you that bandwidth is the most relevant
service guarantee for I/O in desktops and the like, prove that
bandwidth is the most important service guarantee in servers too.

Again, all the examples I can think of seem to confirm it:
. file hosting: a good service must guarantee reasonable read/write,
i.e., download/upload, speeds to users
. file streaming: a good service must guarantee low drop rates, and
this can be guaranteed only by guaranteeing bandwidth and latency
. web hosting: high bandwidth and low latency needed here too
. clouds: high bw and low latency needed to let, e.g., users of VMs
enjoy high responsiveness and, for example, reasonable file-copy
time
...

To put in yet another way, with packet I/O in, e.g., clouds, there are
basically the same issues, and the main goal is again guaranteeing
bandwidth and low latency among nodes.

Could you please provide a concrete server example (assuming we still
agree about desktops), where I/O bandwidth does not matter while time
does?

>> Could you please suggest me some test to show how sector-based
>> guarantees fails?
> 
> Well, mix 4k random and sequential workloads and try to distribute the
> acteual IO resources.
> 

If I'm not mistaken, we have already gone through this example too,
and I thought we agreed on what service scheme worked best, again
focusing only on desktops.  To make a long story short(er), here is a
snippet from one of our last exchanges.

----------

On Sat, Apr 16, 2016 at 12:08:44AM +0200, Paolo Valente wrote:
> Maybe the source of confusion is the fact that a simple sector-based,
> proportional share scheduler always distributes total bandwidth
> according to weights. The catch is the additional BFQ rule: random
> workloads get only time isolation, and are charged for full budgets,
> so as to not affect the schedule of quasi-sequential workloads. So,
> the correct claim for BFQ is that it distributes total bandwidth
> according to weights (only) when all competing workloads are
> quasi-sequential. If some workloads are random, then these workloads
> are just time scheduled. This does break proportional-share bandwidth
> distribution with mixed workloads, but, much more importantly, saves
> both total throughput and individual bandwidths of quasi-sequential
> workloads.
> 
> We could then check whether I did succeed in tuning timeouts and
> budgets so as to achieve the best tradeoffs. But this is probably a
> second-order problem as of now.

[you] Ah, I see.  Yeah, that clears it up for me.  I'm gonna play with
cgroup settings and see how it actually behaves.

---------

Why does the above argument not work for a server too?  What am I
missing?

Thanks,
Paolo

> Thanks.
> 
> -- 
> tejun

--
Paolo Valente
Algogroup
Dipartimento di Scienze Fisiche, Informatiche e Matematiche
Via Campi 213/B
41125 Modena - Italy
http://algogroup.unimore.it/people/paolo/

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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