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From: "Toke Høiland-Jørgensen" <>
To: Tejun Heo <>,,,,,,,
Cc:,,,,,,,,,, Tejun Heo <>,
	Josef Bacik <>
Subject: Re: [PATCH 08/10] blkcg: implement blk-ioweight
Date: Fri, 14 Jun 2019 14:17:45 +0200
Message-ID: <> (raw)
In-Reply-To: <>

Tejun Heo <> writes:

> This patchset implements IO cost model based work-conserving
> proportional controller.
> While io.latency provides the capability to comprehensively prioritize
> and protect IOs depending on the cgroups, its protection is binary -
> the lowest latency target cgroup which is suffering is protected at
> the cost of all others.  In many use cases including stacking multiple
> workload containers in a single system, it's necessary to distribute
> IO capacity with better granularity.
> One challenge of controlling IO resources is the lack of trivially
> observable cost metric.  The most common metrics - bandwidth and iops
> - can be off by orders of magnitude depending on the device type and
> IO pattern.  However, the cost isn't a complete mystery.  Given
> several key attributes, we can make fairly reliable predictions on how
> expensive a given stream of IOs would be, at least compared to other
> IO patterns.
> The function which determines the cost of a given IO is the IO cost
> model for the device.  This controller distributes IO capacity based
> on the costs estimated by such model.  The more accurate the cost
> model the better but the controller adapts based on IO completion
> latency and as long as the relative costs across differents IO
> patterns are consistent and sensible, it'll adapt to the actual
> performance of the device.
> Currently, the only implemented cost model is a simple linear one with
> a few sets of default parameters for different classes of device.
> This covers most common devices reasonably well.  All the
> infrastructure to tune and add different cost models is already in
> place and a later patch will also allow using bpf progs for cost
> models.
> Please see the top comment in blk-ioweight.c and documentation for
> more details.

Reading through the description here and in the comment, and with the
caveat that I am familiar with network packet scheduling but not with
the IO layer, I think your approach sounds quite reasonable; and I'm
happy to see improvements in this area!

One question: How are equal-weight cgroups scheduled relative to each
other? Or requests from different processes within a single cgroup for
that matter? FIFO? Round-robin? Something else?



  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14  1:56 [PATCHSET block/for-next] IO cost model based work-conserving porportional controller Tejun Heo
2019-06-14  1:56 ` [PATCH 01/10] blkcg: pass @q and @blkcg into blkcg_pol_alloc_pd_fn() Tejun Heo
2019-06-14  1:56 ` [PATCH 02/10] blkcg: make ->cpd_init_fn() optional Tejun Heo
2019-06-14  1:56 ` [PATCH 03/10] blkcg: separate blkcg_conf_get_disk() out of blkg_conf_prep() Tejun Heo
2019-06-14  1:56 ` [PATCH 04/10] block/rq_qos: add rq_qos_merge() Tejun Heo
2019-06-14  1:56 ` [PATCH 05/10] block/rq_qos: implement rq_qos_ops->queue_depth_changed() Tejun Heo
2019-06-14  1:56 ` [PATCH 06/10] blkcg: s/RQ_QOS_CGROUP/RQ_QOS_LATENCY/ Tejun Heo
2019-06-14  1:56 ` [PATCH 07/10] blk-mq: add optional request->pre_start_time_ns Tejun Heo
2019-06-14  1:56 ` [PATCH 08/10] blkcg: implement blk-ioweight Tejun Heo
2019-06-14 12:17   ` Toke Høiland-Jørgensen [this message]
2019-06-14 15:09     ` Tejun Heo
2019-06-14 20:50       ` Toke Høiland-Jørgensen
2019-06-15 15:57         ` Tejun Heo
2019-06-14  1:56 ` [PATCH 09/10] blkcg: add tools/cgroup/ Tejun Heo
2019-06-14  1:56 ` [PATCH 10/10] blkcg: implement BPF_PROG_TYPE_IO_COST Tejun Heo
2019-06-14 11:32   ` Quentin Monnet
2019-06-14 14:52     ` Tejun Heo
2019-06-14 16:35       ` Alexei Starovoitov
2019-06-14 17:09         ` Tejun Heo
2019-06-14 17:56 ` [PATCHSET block/for-next] IO cost model based work-conserving porportional controller Tejun Heo

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