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SubjectRe: [PATCH RFC 01/14] block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler

> Il giorno 05 mar 2017, alle ore 16:16, Jens Axboe <> ha scritto:
> On 03/04/2017 09:01 AM, Paolo Valente wrote:
>> We tag as v0 the version of BFQ containing only BFQ's engine plus
>> hierarchical support. BFQ's engine is introduced by this commit, while
>> hierarchical support is added by next commit. We use the v0 tag to
>> distinguish this minimal version of BFQ from the versions containing
>> also the features and the improvements added by next commits. BFQ-v0
>> coincides with the version of BFQ submitted a few years ago [1], apart
>> from the introduction of preemption, described below.
>> BFQ is a proportional-share I/O scheduler, whose general structure,
>> plus a lot of code, are borrowed from CFQ.
> I'll take a closer look at this in the coming week.


> But one quick
> comment - don't default to BFQ. Both because it might not be fully
> stable yet, and also because the performance limitation of it is
> quite severe. Whereas deadline doesn't really hurt single queue
> flash at all, BFQ will.

Ok, sorry. I was doubtful on what to do, but, to not bother you on
every details, I went for setting it as default, because I thought
people would have preferred to test it, even from boot, in this
preliminary stage. I reset elevator.c in the submission, unless you
want me to do it even before receiving your and others' reviews.

> Generally, I think that sort of logic should go into a udev rule. If
> a device is rotational it should default to BFQ once the dust has
> settled.


Looking forward for your feedback,

> --
> Jens Axboe

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