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From: Paolo Valente <paolo.valente@linaro.org>
To: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	Fabio Checconi <fchecconi@gmail.com>,
	Arianna Avanzini <avanzini.arianna@gmail.com>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	ulf.hansson@linaro.org, linus.walleij@linaro.org,
	broonie@kernel.org
Subject: Re: [PATCH RFC 10/22] block, bfq: add full hierarchical scheduling and cgroups support
Date: Fri, 6 May 2016 22:20:18 +0200	[thread overview]
Message-ID: <2D83ACA0-2513-4019-9A0D-3166FDDE7485@linaro.org> (raw)
In-Reply-To: <571E7E63.6010103@linaro.org>


Il giorno 25/apr/2016, alle ore 22:30, Paolo <paolo.valente@linaro.org> ha scritto:

> Il 25/04/2016 21:24, Tejun Heo ha scritto:
>> Hello, Paolo.
>> 
> 
> Hi
> 
>> On Sat, Apr 23, 2016 at 09:07:47AM +0200, Paolo Valente wrote:
>>> There is certainly something I don’t know here, because I don’t
>>> understand why there is also a workqueue containing root-group I/O
>>> all the time, if the only process doing I/O belongs to a different
>>> (sub)group.
>> 
>> Hmmm... maybe metadata updates?
>> 
> 
> That's what I thought in the first place. But one half or one third of
> the IOs sounded too much for metadata (the percentage varies over time
> during the test). And root-group IOs are apparently large. Here is an
> excerpt from the output of
> 
> grep -B 1 insert_request trace
> 
>    kworker/u8:4-116   [002] d...   124.349971:   8,0    I   W 3903488 + 1024 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.349978:   8,0    m   N cfq409A  / insert_request
> --
>    kworker/u8:4-116   [002] d...   124.350770:   8,0    I   W 3904512 + 1200 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.350780:   8,0    m   N cfq96A /seq_write insert_request
> --
>    kworker/u8:4-116   [002] d...   124.363911:   8,0    I   W 3905712 + 1888 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.363916:   8,0    m   N cfq409A  / insert_request
> --
>    kworker/u8:4-116   [002] d...   124.364467:   8,0    I   W 3907600 + 352 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.364474:   8,0    m   N cfq96A /seq_write insert_request
> --
>    kworker/u8:4-116   [002] d...   124.369435:   8,0    I   W 3907952 + 1680 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.369439:   8,0    m   N cfq96A /seq_write insert_request
> --
>    kworker/u8:4-116   [002] d...   124.369441:   8,0    I   W 3909632 + 560 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.369442:   8,0    m   N cfq96A /seq_write insert_request
> --
>    kworker/u8:4-116   [002] d...   124.373299:   8,0    I   W 3910192 + 1760 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.373301:   8,0    m   N cfq409A  / insert_request
> --
>    kworker/u8:4-116   [002] d...   124.373519:   8,0    I   W 3911952 + 480 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.373522:   8,0    m   N cfq96A /seq_write insert_request
> --
>    kworker/u8:4-116   [002] d...   124.381936:   8,0    I   W 3912432 + 1728 [kworker/u8:4]
>    kworker/u8:4-116   [002] d...   124.381937:   8,0    m   N cfq409A / insert_request
> 
> 
>>> Anyway, if this is expected, then there is no reason to bother you
>>> further on it. In contrast, the actual problem I see is the
>>> following. If one third or half of the bios belong to a different
>>> group than the writer that one wants to isolate, then, whatever
>>> weight is assigned to the writer group, we will never be able to let
>>> the writer get the desired share of the time (or of the bandwidth
>>> with bfq and all quasi-sequential workloads). For instance, in the
>>> scenario that you told me to try, the writer will never get 50% of
>>> the time, with any scheduler. Am I missing something also on this?
>> 
>> While a worker may jump across different cgroups, the IOs are still
>> coming from somewhere and if the only IO generator on the machine is
>> the test dd, the bios from that cgroup should dominate the IOs.  I
>> think it'd be helpful to investigate who's issuing the root cgroup
>> IOs.
>> 
> 

I can now confirm that, because of a little bug, a fraction ranging
from one third to half of the writeback bios for the writer is wrongly
associated with the root group. I'm sending a bugfix.

I'm retesting BFQ after this blk fix. If I understand correctly, now
you agree that BFQ is well suited for cgroups too, at least in
principle. So I will apply all your suggestions and corrections, and
submit a fresh patchset.

Thanks,
Paolo

> Ok (if there is some quick way to get this information without
> instrumenting the code, then any suggestion or pointer is welcome).
> 
> Thanks,
> Paolo
> 
>> Thanks.

  reply	other threads:[~2016-05-06 20:20 UTC|newest]

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-01 22:12 [PATCH RFC 00/22] Replace the CFQ I/O Scheduler with BFQ Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 01/22] block, cfq: remove queue merging for close cooperators Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 02/22] block, cfq: remove close-based preemption Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 03/22] block, cfq: remove deep seek queues logic Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 04/22] block, cfq: remove SSD-related logic Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 05/22] block, cfq: get rid of hierarchical support Paolo Valente
2016-02-10 23:04   ` Tejun Heo
2016-02-01 22:12 ` [PATCH RFC 06/22] block, cfq: get rid of queue preemption Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 07/22] block, cfq: get rid of workload type Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 08/22] block, cfq: get rid of latency tunables Paolo Valente
2016-02-10 23:05   ` Tejun Heo
2016-02-01 22:12 ` [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente
2016-02-11 22:22   ` Tejun Heo
2016-02-12  0:35     ` Mark Brown
2016-02-17 15:57       ` Tejun Heo
2016-02-17 16:02         ` Mark Brown
2016-02-17 17:04           ` Tejun Heo
2016-02-17 18:13             ` Jonathan Corbet
2016-02-17 19:45               ` Tejun Heo
2016-02-17 19:56                 ` Jonathan Corbet
2016-02-17 20:14                   ` Tejun Heo
2016-02-17  9:02     ` Paolo Valente
2016-02-17 17:02       ` Tejun Heo
2016-02-20 10:23         ` Paolo Valente
2016-02-20 11:02           ` Paolo Valente
2016-03-01 18:46           ` Tejun Heo
2016-03-04 17:29             ` Linus Walleij
2016-03-04 17:39               ` Christoph Hellwig
2016-03-04 18:10                 ` Austin S. Hemmelgarn
2016-03-11 11:16                   ` Christoph Hellwig
2016-03-11 13:38                     ` Austin S. Hemmelgarn
2016-03-05 12:18                 ` Linus Walleij
2016-03-11 11:17                   ` Christoph Hellwig
2016-03-11 11:24                     ` Nikolay Borisov
2016-03-11 11:49                       ` Christoph Hellwig
2016-03-11 14:53                     ` Linus Walleij
2016-03-09  6:55                 ` Paolo Valente
2016-04-13 19:54                 ` Tejun Heo
2016-04-14  5:03                   ` Mark Brown
2016-03-09  6:34             ` Paolo Valente
2016-04-13 20:41               ` Tejun Heo
2016-04-14 10:23                 ` Paolo Valente
2016-04-14 16:29                   ` Tejun Heo
2016-04-15 14:20                     ` Paolo Valente
2016-04-15 15:08                       ` Tejun Heo
2016-04-15 16:17                         ` Paolo Valente
2016-04-15 19:29                           ` Tejun Heo
2016-04-15 22:08                             ` Paolo Valente
2016-04-15 22:45                               ` Tejun Heo
2016-04-16  6:03                                 ` Paolo Valente
2016-04-15 14:49                     ` Linus Walleij
2016-02-01 22:12 ` [PATCH RFC 10/22] block, bfq: add full hierarchical scheduling and cgroups support Paolo Valente
2016-02-11 22:28   ` Tejun Heo
2016-02-17  9:07     ` Paolo Valente
2016-02-17 17:14       ` Tejun Heo
2016-02-17 17:45         ` Tejun Heo
2016-04-20  9:32     ` Paolo
2016-04-22 18:13       ` Tejun Heo
2016-04-22 18:19         ` Paolo Valente
2016-04-22 18:41           ` Tejun Heo
2016-04-22 19:05             ` Paolo Valente
2016-04-22 19:32               ` Tejun Heo
2016-04-23  7:07                 ` Paolo Valente
2016-04-25 19:24                   ` Tejun Heo
2016-04-25 20:30                     ` Paolo
2016-05-06 20:20                       ` Paolo Valente [this message]
2016-05-12 13:11                         ` Paolo
2016-07-27 16:13                         ` [PATCH RFC V8 00/22] Replace the CFQ I/O Scheduler with BFQ Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 01/22] block, cfq: remove queue merging for close cooperators Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 02/22] block, cfq: remove close-based preemption Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 03/22] block, cfq: remove deep seek queues logic Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 04/22] block, cfq: remove SSD-related logic Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 05/22] block, cfq: get rid of hierarchical support Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 06/22] block, cfq: get rid of queue preemption Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 07/22] block, cfq: get rid of workload type Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 08/22] block, cfq: get rid of latency tunables Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 10/22] block, bfq: add full hierarchical scheduling and cgroups support Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 11/22] block, bfq: improve throughput boosting Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 12/22] block, bfq: modify the peak-rate estimator Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 13/22] block, bfq: add more fairness with writes and slow processes Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 14/22] block, bfq: improve responsiveness Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 15/22] block, bfq: reduce I/O latency for soft real-time applications Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 16/22] block, bfq: preserve a low latency also with NCQ-capable drives Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 17/22] block, bfq: reduce latency during request-pool saturation Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 18/22] block, bfq: add Early Queue Merge (EQM) Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 19/22] block, bfq: reduce idling only in symmetric scenarios Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 20/22] block, bfq: boost the throughput on NCQ-capable flash-based devices Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 21/22] block, bfq: boost the throughput with random I/O on NCQ-capable HDDs Paolo Valente
2016-07-27 16:13                           ` [PATCH RFC V8 22/22] block, bfq: handle bursts of queue activations Paolo Valente
2016-07-28 16:50                           ` [PATCH RFC V8 00/22] Replace the CFQ I/O Scheduler with BFQ Paolo
2016-02-01 22:12 ` [PATCH RFC 11/22] block, bfq: improve throughput boosting Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 12/22] block, bfq: modify the peak-rate estimator Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 13/22] block, bfq: add more fairness to boost throughput and reduce latency Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 14/22] block, bfq: improve responsiveness Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 15/22] block, bfq: reduce I/O latency for soft real-time applications Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 16/22] block, bfq: preserve a low latency also with NCQ-capable drives Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 17/22] block, bfq: reduce latency during request-pool saturation Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 18/22] block, bfq: add Early Queue Merge (EQM) Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 19/22] block, bfq: reduce idling only in symmetric scenarios Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 20/22] block, bfq: boost the throughput on NCQ-capable flash-based devices Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 21/22] block, bfq: boost the throughput with random I/O on NCQ-capable HDDs Paolo Valente
2016-02-01 22:12 ` [PATCH RFC 22/22] block, bfq: handle bursts of queue activations Paolo Valente

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