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SubjectRe: [PATCH 0/3] BFQ I/O Scheduler (second take)
CC: Linux Containers <containers@lists.linux-foundation.org>
Vivek Goyal <vgoyal@redhat.com>

Fabio Checconi wrote:
> Hi Jens, hi all,
>

Hi Fabio,

> this is an updated version of the patchset introducing the BFQ (Budget
> Fair Queueing) I/O scheduler. It is based on CFQ and it has been
> developed trying to improve the predictability and the fairness of the
> service prvided, without penalizing the aggregate throughput.
>
> This new version hopefully addresses the issues pointed out after the
> first submission[1]:
>
> 1) it introduces a bitmap to notify priority changes to the bfq/cfq;
> 2) it introduces a timeout to put an higher limit to the time a
> task can take to consume its budget;
> 3) it supports hierarchical scheduling.
>

So this is another cgroup-aware block i/o controller. ;)

People are sending different proposals for bio controller. A summary
on this can be found here:
http://marc.info/?l=linux-kernel&m=121798534716673&w=2

And a new proposal sent by Vivek several days ago:
http://lkml.org/lkml/2008/11/6/227

And there are some discussions about can we modify the elevator layer
and create a common layer so we can provide group control for all
the 4 io schedulers. (in the above mail thread)

You may share some ideas with us.

> With the introduction of a budget timeout, each task is still assigned
> a budget measured in number of sectors instead of amount of time,
> but a budget is not served to its exhaustion if it's taking too much
> to complete. Budgets are still scheduled using a modified version
> of WF2Q+.
>
> Using huge values for max_budget turns the scheduler into a pure
> time-domain proportional share one, and the timeout controls the duration
> of the time quanta.
>
> WRT the support for hierarchical scheduling, that is being discussed
> so much in these days, this scheduler does not add anything new, it
> supports proportional share distribution of disk bandwidth among
> full cgroup hierarchies; the mapping from requests to cgroups is
> correct only in case of synchronous reads.
>
> The overall diffstat is the following:
>
> block/Kconfig.iosched | 25 +
> block/Makefile | 1 +
> block/bfq-cgroup.c | 743 +++++++++++++++
> block/bfq-ioc.c | 375 ++++++++
> block/bfq-iosched.c | 2010 +++++++++++++++++++++++++++++++++++++++++
> block/bfq-sched.c | 950 +++++++++++++++++++
> block/bfq.h | 514 +++++++++++
> block/blk-ioc.c | 27 +-
> block/cfq-iosched.c | 10 +-
> fs/ioprio.c | 9 +-
> include/linux/cgroup_subsys.h | 6 +
> include/linux/iocontext.h | 18 +-
> 12 files changed, 4669 insertions(+), 19 deletions(-)
>
> For a complete description of the algorithm and of its properties
> please refer to [2], (where extensive experiments on older hw can
> also be found), and for some performance measurements and implementation
> details, to [3].
>
> [1] http://lkml.org/lkml/2008/4/1/234
> [2] http://algo.ing.unimo.it/people/paolo/disk_sched/
> [3] http://feanor.sssup.it/~fabio/linux/bfq/
>
> As usual, any kind of feedback will be greatly appreciated, thanks
> in advance.
>
> Fabio Checconi, Paolo Valente



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