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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, newella@fb.com, clm@fb.com,
	josef@toxicpanda.com, dennisz@fb.com, lizefan@huawei.com,
	hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
	linux-block@vger.kernel.org, kernel-team@fb.com,
	cgroups@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
	kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
	bpf@vger.kernel.org, Josef Bacik <jbacik@fb.com>
Subject: Re: [PATCH 08/10] blkcg: implement blk-ioweight
Date: Fri, 14 Jun 2019 22:50:34 +0200	[thread overview]
Message-ID: <87blyzc2n9.fsf@toke.dk> (raw)
In-Reply-To: <20190614150924.GB538958@devbig004.ftw2.facebook.com>

Tejun Heo <tj@kernel.org> writes:

> Hello, Toke.
>
> On Fri, Jun 14, 2019 at 02:17:45PM +0200, Toke Høiland-Jørgensen wrote:
>> 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?
>
> Once each cgroup got their hierarchical weight and current vtime for
> the period, they don't talk to each other.  Each is expected to do the
> right thing on their own.  When the period ends, the timer looks at
> how the device is performing, how much each used and so on and then
> make necessary adjustments.  So, there's no direct cross-cgroup
> synchronization.  Each is throttled to their target level
> independently.

Right, makes sense.

> Within a single cgroup, the IOs are FIFO. When an IO has enough vtime
> credit, it just passes through. When it doesn't, it always waits
> behind any other IOs which are already waiting.

OK. Is there any fundamental reason why requests from individual
processes could not be interleaved? Or does it just not give the same
benefits in an IO request context as it does for network packets?

Thanks for the explanations! :)

-Toke

  reply	other threads:[~2019-06-14 20:50 UTC|newest]

Thread overview: 34+ 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
2019-06-14 15:09     ` Tejun Heo
2019-06-14 20:50       ` Toke Høiland-Jørgensen [this message]
2019-06-15 15:57         ` Tejun Heo
2019-06-14  1:56 ` [PATCH 09/10] blkcg: add tools/cgroup/monitor_ioweight.py 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
2019-08-20 10:48   ` Paolo Valente
2019-08-20 15:04     ` Paolo Valente
2019-08-20 15:19       ` Tejun Heo
2019-08-22  8:58         ` Paolo Valente
2019-08-31  6:53           ` Tejun Heo
2019-08-31  7:10             ` Paolo Valente
2019-08-31 11:20               ` Tejun Heo
2019-09-02 15:45             ` Paolo Valente
2019-09-02 15:56               ` Tejun Heo
2019-09-02 19:43                 ` Paolo Valente
2019-09-05 16:55                   ` Tejun Heo
2019-09-06  9:07                     ` Paolo Valente
2019-09-06 14:58                       ` Tejun Heo
2020-02-19 18:34                         ` Paolo Valente

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